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.

Consecutive palmitoylation and phosphorylation orchestrates NLRP3 membrane trafficking and inflammasome activation.

NLRP3 inflammasome activation, essential for cytokine secretion and pyroptosis in response to diverse stimuli, is closely associated with various diseases. Upon stimulation, NLRP3 undergoes subcellular membrane trafficking and conformational rearrangements, preparing itself for inflammasome assembly at the microtubule-organizing center (MTOC). Here, we elucidate an orchestrated mechanism underlying these ordered processes using human and murine cells. Specifically, NLRP3 undergoes palmitoylation at two sites by palmitoyl transferase zDHHC1, facilitating its trafficking between subcellular membranes, including the mitochondria, trans-Golgi network (TGN), and endosome. This dynamic trafficking culminates in the localization of NLRP3 to the MTOC, where LATS1/2, pre-recruited to MTOC during priming, phosphorylates NLRP3 to further facilitate its interaction with NIMA-related kinase 7 (NEK7), ultimately leading to full NLRP3 activation. Consistently, Zdhhc1-deficiency mitigated LPS-induced inflammation and conferred protection against mortality in mice. Altogether, our findings provide valuable insights into the regulation of NLRP3 membrane trafficking and inflammasome activation, governed by palmitoylation and phosphorylation events.

The Hippo Pathway Kinases LATS1/2 Suppress Cancer Immunity.

Poorly immunogenic tumor cells evade host immunity and grow even in the presence of an intact immune system, but the complex mechanisms regulating tumor immunogenicity have not been elucidated. Here, we discovered an unexpected role of the Hippo pathway in suppressing anti-tumor immunity. We demonstrate that, in three different murine syngeneic tumor models (B16, SCC7, and 4T1), loss of the Hippo pathway kinases LATS1/2 (large tumor suppressor 1 and 2) in tumor cells inhibits tumor growth. Tumor regression by LATS1/2 deletion requires adaptive immune responses, and LATS1/2 deficiency enhances tumor vaccine efficacy. Mechanistically, LATS1/2-null tumor cells secrete nucleic-acid-rich extracellular vesicles, which induce a type I interferon response via the Toll-like receptors-MYD88/TRIF pathway. LATS1/2 deletion in tumors thus improves tumor immunogenicity, leading to tumor destruction by enhancing anti-tumor immune responses. Our observations uncover a key role of the Hippo pathway in modulating tumor immunogenicity and demonstrate a proof of concept for targeting LATS1/2 in cancer immunotherapy.

WWC proteins mediate LATS1/2 activation by Hippo kinases and imply a tumor suppression strategy.

YAP and TAZ (YAP/TAZ), two major effectors of the Hippo signaling pathway, are frequently activated in human cancers. The activity of YAP/TAZ is strictly repressed upon phosphorylation by LATS1/2 tumor suppressors. However, it is unclear how LATS1/2 are precisely regulated by upstream factors such as Hippo kinases MST1/2. Here, we show that WWC proteins (WWC1/2/3) directly interact with LATS1/2 and SAV1, and SAV1, in turn, brings in MST1/2 to phosphorylate and activate LATS1/2. Hence, WWC1/2/3 play an organizer role in a signaling module that mediates LATS1/2 activation by MST1/2. Moreover, we have defined a minimum protein interaction interface on WWC1/2/3 that is sufficient to activate LATS1/2 in a robust and specific manner. The corresponding minigene, dubbed as SuperHippo, can effectively suppress tumorigenesis in multiple tumor models. Our study has uncovered a molecular mechanism underlying LATS1/2 regulation and provides a strategy for treating diverse malignancies related to Hippo pathway dysregulation.

LATS1 controls CTCF chromatin occupancy and hormonal response of 3D-grown breast cancer cells.

The cancer epigenome has been studied in cells cultured in two-dimensional (2D) monolayers, but recent studies highlight the impact of the extracellular matrix and the three-dimensional (3D) environment on multiple cellular functions. Here, we report the physical, biochemical, and genomic differences between T47D breast cancer cells cultured in 2D and as 3D spheroids. Cells within 3D spheroids exhibit a rounder nucleus with less accessible, more compacted chromatin, as well as altered expression of ~2000 genes, the majority of which become repressed. Hi-C analysis reveals that cells in 3D are enriched for regions belonging to the B compartment, have decreased chromatin-bound CTCF and increased fusion of topologically associating domains (TADs). Upregulation of the Hippo pathway in 3D spheroids results in the activation of the LATS1 kinase, which promotes phosphorylation and displacement of CTCF from DNA, thereby likely causing the observed TAD fusions. 3D cells show higher chromatin binding of progesterone receptor (PR), leading to an increase in the number of hormone-regulated genes. This effect is in part mediated by LATS1 activation, which favors cytoplasmic retention of YAP and CTCF removal.

Hippo pathway inactivation through subcellular localization of NF2/merlin in outer cells of mouse embryos.

The Hippo pathway plays a crucial role in cell proliferation and differentiation during tumorigenesis, tissue homeostasis and early embryogenesis. Scaffold proteins from the ezrin-radixin-moesin (ERM) family, including neurofibromin 2 (NF2; Merlin), regulate the Hippo pathway through cell polarity. However, the mechanisms underlying Hippo pathway regulation via cell polarity in establishing outer cells remain unclear. In this study, we generated artificial Nf2 mutants in the N-terminal FERM domain (L64P) and examined Hippo pathway activity by assessing the subcellular localization of YAP1 in early embryos expressing these mutant mRNAs. The L64P-Nf2 mutant inhibited NF2 localization around the cell membrane, resulting in YAP1 cytoplasmic translocation in the polar cells. L64P-Nf2 expression also disrupted the apical centralization of both large tumor suppressor 2 (LATS2) and ezrin in the polar cells. Furthermore, Lats2 mutants in the FERM binding domain (L83K) inhibited YAP1 nuclear translocation. These findings demonstrate that NF2 subcellular localization mediates cell polarity establishment involving ezrin centralization. This study provides previously unreported insights into how the orchestration of the cell-surface components, including NF2, LATS2 and ezrin, modulates the Hippo pathway during cell polarization.

Regulation of the Hippo Pathway by Phosphatidic Acid-Mediated Lipid-Protein Interaction.

The Hippo pathway plays a crucial role in organ size control and tumor suppression, but its precise regulation is not fully understood. In this study, we discovered that phosphatidic acid (PA)-related lipid signaling is a key regulator of the Hippo pathway. Supplementing PA in various Hippo-activating conditions activates YAP. This PA-related lipid signaling is involved in Rho-mediated YAP activation. Mechanistically, PA directly interacts with Hippo components LATS and NF2 to disrupt LATS-MOB1 complex formation and NF2-mediated LATS membrane translocation and activation, respectively. Inhibition of phospholipase D (PLD)-dependent PA production suppresses YAP oncogenic activities. PLD1 is highly expressed in breast cancer and positively correlates with YAP activation, suggesting their pathological relevance in breast cancer development. Taken together, our study not only reveals a role of PLD-PA lipid signaling in regulating the Hippo pathway but also indicates that the PLD-PA-YAP axis is a potential therapeutic target for cancer treatment.

LATS1/2 control TGFB-directed epithelial-to-mesenchymal transition in the murine dorsal cranial neuroepithelium through YAP regulation.

Hippo signaling, an evolutionarily conserved kinase cascade involved in organ size control, plays key roles in various tissue developmental processes, but its role in craniofacial development remains poorly understood. Using the transgenic Wnt1-Cre2 driver, we inactivated the Hippo signaling components Lats1 and Lats2 in the cranial neuroepithelium of mouse embryos and found that the double conditional knockout (DCKO) of Lats1/2 resulted in neural tube and craniofacial defects. Lats1/2 DCKO mutant embryos had microcephaly with delayed and defective neural tube closure. Furthermore, neuroepithelial cell shape and architecture were disrupted within the cranial neural tube in Lats1/2 DCKO mutants. RNA sequencing of embryonic neural tubes revealed increased TGFB signaling in Lats1/2 DCKO mutants. Moreover, markers of epithelial-to-mesenchymal transition (EMT) were upregulated in the cranial neural tube. Inactivation of Hippo signaling downstream effectors, Yap and Taz, suppressed neuroepithelial defects, aberrant EMT and TGFB upregulation in Lats1/2 DCKO embryos, indicating that LATS1/2 function via YAP and TAZ. Our findings reveal important roles for Hippo signaling in modulating TGFB signaling during neural crest EMT.

Reanalysis of single-cell RNA sequencing data does not support herpes simplex virus 1 latency in non-neuronal ganglionic cells in mice.

Most individuals are latently infected with herpes simplex virus type 1 (HSV-1), and it is well-established that HSV-1 establishes latency in sensory neurons of peripheral ganglia. However, it was recently proposed that latent HSV-1 is also present in immune cells recovered from the ganglia of experimentally infected mice. Here, we reanalyzed the single-cell RNA sequencing (scRNA-Seq) data that formed the basis for that conclusion. Unexpectedly, off-target priming in 3' scRNA-Seq experiments enabled the detection of non-polyadenylated HSV-1 latency-associated transcript (LAT) intronic RNAs. However, LAT reads were near-exclusively detected in mixed populations of cells undergoing cell death. Specific loss of HSV-1 LAT and neuronal transcripts during quality control filtering indicated widespread destruction of neurons, supporting the presence of contaminating cell-free RNA in other cells following tissue processing. In conclusion, the reported detection of latent HSV-1 in non-neuronal cells is best explained using compromised scRNA-Seq datasets.IMPORTANCEMost people are infected with herpes simplex virus type 1 (HSV-1) during their life. Once infected, the virus generally remains in a latent (silent) state, hiding within the neurons of peripheral ganglia. Periodic reactivation (reawakening) of the virus may cause fresh diseases such as cold sores. A recent study using single-cell RNA sequencing (scRNA-Seq) proposed that HSV-1 can also establish latency in the immune cells of mice, challenging existing dogma. We reanalyzed the data from that study and identified several flaws in the methodologies and analyses performed that invalidate the published conclusions. Specifically, we showed that the methodologies used resulted in widespread destruction of neurons which resulted in the presence of contaminants that confound the data analysis. We thus conclude that there remains little to no evidence for HSV-1 latency in immune cells.

Lats1 and Lats2 regulate YAP and TAZ activity to control the development of mouse Sertoli cells.

Recent reports suggest that the Hippo signaling pathway regulates testis development, though its exact roles in Sertoli cell differentiation remain unknown. Here, we examined the functions of the main Hippo pathway kinases, large tumor suppressor homolog kinases 1 and 2 (Lats1 and Lats2) in developing mouse Sertoli cells. Conditional inactivation of Lats1/2 in Sertoli cells resulted in the disorganization and overgrowth of the testis cords, the induction of a testicular inflammatory response and germ cell apoptosis. Stimulated by retinoic acid 8 (STRA8) expression in germ cells additionally suggested that germ cells may have been preparing to enter meiosis prior to their loss. Gene expression analyses of the developing testes of conditional knockout animals further suggested impaired Sertoli cell differentiation, epithelial-to-mesenchymal transition, and the induction of a specific set of genes associated with Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ)-mediated integrin signaling. Finally, the involvement of YAP/TAZ in Sertoli cell differentiation was confirmed by concomitantly inactivating Yap/Taz in Lats1/2 conditional knockout model, which resulted in a partial rescue of the testicular phenotypic changes. Taken together, these results identify Hippo signaling as a crucial pathway for Sertoli cell development and provide novel insight into Sertoli cell fate maintenance.

Liquid-Liquid Phase Separation of DDR1 Counteracts the Hippo Pathway to Orchestrate Arterial Stiffening.

BACKGROUND: The Hippo-YAP (yes-associated protein) signaling pathway is modulated in response to various environmental cues. Activation of YAP in vascular smooth muscle cells conveys the extracellular matrix stiffness-induced changes in vascular smooth muscle cells phenotype and behavior. Recent studies have established a mechanoreceptive role of receptor tyrosine kinase DDR1 (discoidin domain receptor 1) in vascular smooth muscle cells. METHODS: We conduced 5/6 nephrectomy in vascular smooth muscle cells-specific Ddr1-knockout mice, accompanied by pharmacological inhibition of the Hippo pathway kinase LATS1 (large tumor suppressor 1), to investigate DDR1 in YAP activation. We utilized polyacrylamide gels of varying stiffness or the DDR1 ligand, type I collagen, to stimulate the cells. We employed multiple molecular biological techniques to explore the role of DDR1 in controlling the Hippo pathway and to determine the mechanistic basis by which DDR1 exerts this effect. RESULTS: We identified the requirement for DDR1 in stiffness/collagen-induced YAP activation. We uncovered that DDR1 underwent stiffness/collagen binding-stimulated liquid-liquid phase separation and co-condensed with LATS1 to inactivate LATS1. Mutagenesis experiments revealed that the transmembrane domain is responsible for DDR1 droplet formation. Purified DDR1 N-terminal and transmembrane domain was sufficient to drive its reversible condensation. Depletion of the DDR1 C-terminus led to failure in co-condensation with LATS1. Interaction between the DDR1 C-terminus and LATS1 competitively inhibited binding of MOB1 (Mps one binder 1) to LATS1 and thus the subsequent phosphorylation of LATS1. Introduction of the single-point mutants, histidine-745-proline and histidine-902-proline, to DDR1 on the C-terminus abolished the co-condensation. In mouse models, YAP activity was positively correlated with collagen I expression and arterial stiffness. LATS1 inhibition reactivated the YAP signaling in Ddr1-deficient vessels and abrogated the arterial softening effect of Ddr1 deficiency. CONCLUSIONS: These findings identify DDR1 as a mediator of YAP activation by mechanical and chemical stimuli and demonstrate that DDR1 regulates LATS1 phosphorylation in an liquid-liquid phase separation-dependent manner.

MELK aggravates lung adenocarcinoma by regulating EZH2 ubiquitination and H3K27me3 histone methylation of LATS2.

We tried to elucidate the possible roles of maternal embryonic leucine pull chain kinase (MELK) in lung adenocarcinoma (LUAD) growth and metastasis. Differentially expressed genes in LUAD samples were analysed by the GEPIA database. Clinical tissue samples and cells were collected for MELK, EZH2 and LATS2 expression determination. Co-IP assay was used to verify the interaction between EZH2 and MELK; CHX tracking assay and ubiquitination assay detected the degradation of MELK on EZH2 ubiquitination. ChIP assay detected the enrichment of EZH2 and H3K27me3 on the LATS2 promoter region. LUAD cells were selected for in vitro validation, and the tumorigenic ability of LUAD cells was also observed in a transplantation tumour model of LUAD nude mice. MELK and EZH2 were highly expressed in LUAD samples, while LATS2 was lowly expressed. MELK interacted with EZH2 to inhibit its ubiquitination degradation; EZH2 elevated H3K27me3 modification in the LATS2 promoter to lower LATS2 expression. Silencing MELK or EZH2 or overexpressing LATS2 restrained LUAD cell proliferation and invasion, and facilitated their apoptosis. Silencing MELK or EZH2 or overexpressing LATS2 suppressed tumour formation in nude mice. This study demonstrated that MELK aggravated LUAD by upregulating EZH2 and downregulating LATS2.

m6A-induced TRIB3 regulates Hippo pathway through interacting with LATS1 to promote the progression of lung adenocarcinoma.

Recent studies have indicated that dysregulation of the Hippo/Yes-associated protein (YAP) axis is associated with tumor progression and therapy resistance in various cancer types, including lung adenocarcinoma (LUAD). Understanding the regulation of Hippo signaling in LUAD is of great significance. Elevated levels of TRIB3, a pseudo kinase, have been observed in certain lung malignancies and are associated with an unfavorable prognosis. Our research aims to investigate whether increased TRIB3 levels enhance the malignant characteristics of LUAD cells and tumor progression through its interaction with the Hippo signaling pathway. In this study, we reported a positive correlation between elevated expression of TRIB3 and LUAD progression. Additionally, TRIB3 has the ability to enhance TEAD luciferase function and suppress Hippo pathway activity. Moreover, TRIB3 increases total YAP protein levels and promotes YAP nuclear localization. Mechanistic experiments revealed that TRIB3 directly interacts with large tumor suppressor kinase 1 (LATS1), thereby suppressing Hippo signaling. Moreover, the decrease in METTL3-mediated N6-methyladenosine modification of TRIB3 results in a substantial elevation of its expression levels in LUAD cells. Collectively, our research unveils a novel discovery that TRIB3 enhances the growth and invasion of LUAD cells by interacting with LATS1 and inhibiting the Hippo signaling pathway. TRIB3 may serve as a potential biomarker for an unfavorable prognosis and a target for novel treatments in YAP-driven lung cancer.

Palbociclib sensitizes ER-positive breast cancer cells to fulvestrant by promoting the ubiquitin-mediated degradation of ER-α via SNHG17/Hippo-YAP axis.

PURPOSE: Endocrine therapy is the anti-tumor therapy for human breast cancer but endocrine resistance was a major burden. It has been reported that Palbociclib and fulvestrant can be used in combination for the treatment of patients who are experiencing endocrine resistance. However, the underlying mechanism is unclear. In this study, we aimed to investigate the mechanism by which Palbocicilib affected ER-positive breast cancer, combined with fulvestrant. METHODS: We first detected the effect of palbociclib on cell survival, growth and cycle distribution separately by MTT, colony formation and flow cytometry. Then SNHG17 was screened as palbociclib-targeted LncRNA by LncRNA-seq, and the SNHG17-targeted mRNAs were selected by mRNA-seq for further determination. Subsequently, the underlying mechanism by which palbociclib promoted the cytotoxicity of fulvestrant was confirmed by qRT-PCR, western blot, and immunoprecipitation. Eventually, the xenograft model and immunohistochemistry experiments were used to validate the sensitization effect of palbociclib on fulvestrant and its mechanism in vivo. RESULTS: Palbociclib significantly enhanced the cytotoxicity of fulvestrant in fulvestrant-resistant breast cancer cell lines. Interestingly, this might be related to the lncRNA SNHG17 and the Hippo signaling pathway. And our subsequent western blotting experiments confirmed that overexpressing SNHG17 induced the down-regulation of LATS1 and up-regulated YAP expression. Furthermore, we found that the increased sensitivity of breast cancer cells was closely associated with the LATS1-mediated degradation of ER-α. The following animal experiments also indicated that overexpressing SNHG17 obviously impaired the anti-cancer effect of co-treatment of palbociclib and fulvestrant accompanied by decreased LATS1 and increased ER-α levels. CONCLUSION: Palbociclib might sensitize the cytotoxicity of fulvestrant in ER-positive breast cancer cells by down-regulating SNHG17 expression, and then resulted in the LATS1-inactivated oncogene YAP and LATS1-mediated degradation of ER-α.

Prostaglandin E2 attenuates lung fibroblast differentiation via inactivation of yes-associated protein signaling.

Prostaglandin E2 (PGE2 ) has been implicated in counteracting fibroblast differentiation by TGFß1 during pulmonary fibrosis. However, the precise mechanism is not well understood. We show here that PGE2 via EP2 R and EP4 R inhibits the expression of mechanosensory molecules Lysyl Oxidase Like 2 (LOXL2), myocardin-related transcription factor A (MRTF-A), ECM proteins, plasminogen activation inhibitor 1 (PAI-1), fibronectin (FN), α-smooth muscle actin (α-SMA), and redox sensor (nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (NOX4)) required for TGFß1-mediated fibroblast differentiation. We further demonstrate that PGE2 inhibits fibrotic signaling via Yes-associated protein (YAP) but does so independently from its actions on SMAD phosphorylation and conserved cylindromatosis (CYLD; deubiquitinase) expression. Mechanistically, PGE2 phosphorylates/inactivates YAP downstream of EP2 R/Gαs and restrains its translocation to the nucleus, thus inhibiting its interaction with TEA domain family members (TEADs) and transcription of fibrotic genes. Importantly, pharmacological or siRNA-mediated inhibition of YAP significantly downregulates TGFß1-mediated fibrotic gene expression and myofibroblast formation. Notably, YAP expression is upregulated in the lungs of D. farinae-treated wild type (WT) mice relative to saline-treated WT mice. Our results unravel a unique role for PGE2 -YAP interactions in fibroblast differentiation, and that PGE2 /YAP inhibition can be used as a novel therapeutic target in the treatment of pathological conditions associated with myofibroblasts like asthma.

dMyc-dependent upregulation of CD98 amino acid transporters is required for Drosophila brain tumor growth.

Tumor cells have an increased demand for nutrients to sustain their growth, but how these increased metabolic needs are ensured or how this influences tumor formation and progression remains unclear. To unravel tumor metabolic dependencies, particularly from extracellular metabolites, we have analyzed the role of plasma membrane metabolic transporters in Drosophila brain tumors. Using a well-established neural stem cell-derived tumor model, caused by brat knockdown, we have found that 13 plasma membrane metabolic transporters, including amino acid, carbohydrate and monocarboxylate transporters, are upregulated in tumors and are required for tumor growth. We identified CD98hc and several of the light chains with which it can form heterodimeric amino acid transporters, as crucial players in brat RNAi (brat IR) tumor progression. Knockdown of these components of CD98 heterodimers caused a dramatic reduction in tumor growth. Our data also reveal that the oncogene dMyc is required and sufficient for the upregulation of CD98 transporter subunits in these tumors. Furthermore, tumor-upregulated dmyc and CD98 transporters orchestrate the overactivation of the growth-promoting signaling pathway TOR, forming a core growth regulatory network to support brat IR tumor progression. Our findings highlight the important link between oncogenes, metabolism, and signaling pathways in the regulation of tumor growth and allow for a better understanding of the mechanisms necessary for tumor progression.

RBM24 Suppresses the Tumorigenesis of Glioblastoma by Stabilizing LATS1 mRNA.

The ribose nucleic acid (RNA)-binding motif protein 24 (RBM24) has been recognized as a critical regulatory protein in various types of tumors. However, its specific role in glioblastoma (GBM) has not been thoroughly investigated. The objective of this study is to uncover the role of RBM24 in GBM and understand the underlying mechanism. The expression of RBM24 in GBM was initially analyzed using the Gene Expression Profiling Interactive Analysis (GEPIA). Subsequently, the RBM24 expression levels in clinical samples of GBM were examined, and the survival curves of GBM patients were plotted based on high- and low-expression levels of RBM24 using Kaplan-Meier (KM) plotter. In addition, RBM24 knockdown cell lines and overexpression vectors were created to assess the effects on proliferation, apoptosis, and invasion abilities. Finally, the binding level of RBM24 protein to LATS1 messenger RNA (mRNA) was determined by RNA immunoprecipitation (RIP) assay, and the expression levels of RBM24 and LATS1 were measured through quantitative reverse-transcriptase-polymerase chain reaction (qRT-PCR) and Western blot (WB). Our data revealed a significant decrease in RBM24 mRNA and protein levels in GBM patients, indicating that those with low RBM24 expression had a worse prognosis. Overexpression of RBM24 led to inhibited cell proliferation, reduced invasion, and increased apoptosis in LN229 and U87 cells. In addition, knocking down LATS1 partially reversed the effects of RBM24 on cell proliferation, invasion, and apoptosis in GBM cells. In vivo xenograft model further demonstrated that RBM24 overexpression reduced the growth of subcutaneous tumors in nude mice, accompanied by a decrease in Ki-67 expression and an increase in apoptotic events in tumor tissues. There was also correlation between RBM24 and LATS1 protein expression in the xenograft tumors. RBM24 functions to stabilize LATS1 mRNA, thereby inhibiting the proliferation, suppressing invasion, and promoting apoptosis in GBM cells.

Mechanisms of Hippo pathway regulation.

The Hippo pathway was initially identified in Drosophila melanogaster screens for tissue growth two decades ago and has been a subject extensively studied in both Drosophila and mammals in the last several years. The core of the Hippo pathway consists of a kinase cascade, transcription coactivators, and DNA-binding partners. Recent studies have expanded the Hippo pathway as a complex signaling network with >30 components. This pathway is regulated by intrinsic cell machineries, such as cell-cell contact, cell polarity, and actin cytoskeleton, as well as a wide range of signals, including cellular energy status, mechanical cues, and hormonal signals that act through G-protein-coupled receptors. The major functions of the Hippo pathway have been defined to restrict tissue growth in adults and modulate cell proliferation, differentiation, and migration in developing organs. Furthermore, dysregulation of the Hippo pathway leads to aberrant cell growth and neoplasia. In this review, we focus on recent developments in our understanding of the molecular actions of the core Hippo kinase cascade and discuss key open questions in the regulation and function of the Hippo pathway.

The LATS2 tumor suppressor inhibits SREBP and suppresses hepatic cholesterol accumulation.

The Hippo signaling pathway is a major regulator of organ size. In the liver, Hippo pathway deregulation promotes hyperplasia and hepatocellular carcinoma primarily through hyperactivation of its downstream effector, YAP. The LATS2 tumor suppressor is a core member of the Hippo pathway. A screen for LATS2-interacting proteins in liver-derived cells identified the transcription factor SREBP2, master regulator of cholesterol homeostasis. LATS2 down-regulation caused SREBP activation and accumulation of excessive cholesterol. Likewise, mice harboring liver-specific Lats2 conditional knockout (Lats2-CKO) displayed constitutive SREBP activation and overexpressed SREBP target genes and developed spontaneous fatty liver disease. Interestingly, the impact of LATS2 depletion on SREBP-mediated transcription was clearly distinct from that of YAP overexpression. When challenged with excess dietary cholesterol, Lats2-CKO mice manifested more severe liver damage than wild-type mice. Surprisingly, apoptosis, inflammation, and fibrosis were actually attenuated relative to wild-type mice, in association with impaired p53 activation. Subsequently, Lats2-CKO mice failed to recover effectively from cholesterol-induced damage upon return to a normal diet. Additionally, decreased LATS2 mRNA in association with increased SREBP target gene expression was observed in a subset of human nonalcoholic fatty liver disease cases. Together, these findings further highlight the tight links between tumor suppressors and metabolic homeostasis.

[Effect of Linggui Zhugan Decoction on myocardial fibrosis and Lats1/Yap signaling pathway in mice after myocardial infraction].

This study aims to investigate the effects of Linggui Zhugan Decoction(LGZGD) on myocardial fibrosis(MF) and the Lats1/Yap signaling pathway in mice after myocardial infarction(MI), exploring its role and mechanism in inhibiting MF. The MI-induced ischemic mouse model was established by left anterior descending coronary artery ligation, followed by continuous intervention for six weeks. Doppler ultrasound imaging-system of small animals was used to detect left ventricular ejection fraction(LVEF), left ventricular fractional shortening(LVFS), left ventricular internal diameter at end-systole(LVIDs), and left ventricular internal diameter at end-diastole(LVIDd). Pathological changes in myocardial tissue were observed by HE and Masson staining. Serum levels of creatine kinase isoenzyme MB(CK-MB) and lactate dehydrogenase(LDH) were detected by using ELISA. Myocardial tissue mRNA levels of Lats1, Yap, and connective tissue growth factor(CTGF) were determined by RT-qPCR. Protein expression of alpha-smooth muscle actin(α-SMA), collagen Ⅰ(Col Ⅰ), collagen Ⅲ(Col Ⅲ), tissue inhibitor of metal protease 1(TIMP1), matrix metallopeptidase 2(MMP2), Yap, p-Yap, and n-Yap was determined by Western blot. Compared with the sham group, the model group showed significantly decreased LVEF and LVFS levels, increased LVIDd and LVIDs levels(P<0.01), disordered arrangement of myocardial cells, partial fracture of myocardial fibers, and massive deposition of collagen fibers. Moreover, serum levels of CK-MB and LDH were significantly increased(P<0.01), while myocardial tissue mRNA levels of Lats1 were significantly decreased(P<0.01), and mRNA levels of Yap and CTGF were significantly increased(P<0.01). Protein expression of α-SMA, Col Ⅰ, Col Ⅲ, MMP2, Yap, and n-Yap was significantly increased(P<0.01), while protein expression of Lats1, TIMP1, p-Yap, and the ratio of p-Yap/Yap were significantly decreased(P<0.01). Compared with the model group, after intervention with LGZGD(9.36 g·kg~(-1)), mice showed significantly increased LVEF and LVFS levels, decreased LVIDd and LVIDs levels(P<0.01), more orderly arrangement of myocardial cells, significantly reduced myocardial fiber fracture and collagen fiber deposition. Serum levels of CK-MB and LDH were significantly decreased(P<0.01), while myocardial tissue mRNA levels of Lats1 were significantly increased(P<0.01), and mRNA levels of Yap and CTGF were significantly decreased(P<0.01). Protein expression of α-SMA, Col Ⅰ, Col Ⅲ, MMP2, Yap, and n-Yap was significantly decreased(P<0.01), while protein expression of Lats1, TIMP1, p-Yap, and the ratio of p-Yap/Yap were significantly increased(P<0.01). LGZGD can inhibit MF in mice after MI and improve mouse cardiac function, which is closely related to the activation of the Lats1/Yap signaling pathway.