Human homologue of the Drosophila melanogaster lats tumour suppressor modulates CDC2 activity

The role of yes activated protein (YAP) in melanoma metastasis

Hippo was first identified in a genetic screen as a protein that suppressed proliferation and cell growth. Subsequently, it was shown that hippo acted in a so-called canonical cascade to suppress Yorkie, the Drosophila equivalent of Yes-activated protein (YAP), a mechanosensitive transcriptional cofactor that enhances the activity of the TEAD family of transcription factors. YAP promotes fibrosis, activation of cancer-associated fibroblasts, angiogenesis and cancer cell invasion. YAP activates the expression of the matricellular proteins CCN1 (cyr61) and CCN2 (ctgf), themselves mediators of fibrogenesis and oncogenesis, and coordination of matrix deposition and angiogenesis. This review discusses how therapeutically targeting YAP through YAP inhibitors verteporfin and celastrol and its downstream mediators CCN1 and CCN2 might be useful in treating melanoma.

TPX2 overexpression promotes sensitivity to dasatinib in breast cancer by activating YAP transcriptional signaling

Chromosomal instability (CIN) is a hallmark of cancer aggressiveness, providing genetic plasticity and tumor heterogeneity that allows the tumor to evolve and adapt to stress conditions. CIN is considered a cancer therapeutic biomarker because healthy cells do not exhibit CIN. Despite recent efforts to identify therapeutic strategies related to CIN, the results obtained have been very limited. CIN is characterized by a genetic signature where a collection of genes, mostly mitotic regulators, are overexpressed in CIN-positive tumors, providing aggressiveness and poor prognosis. We attempted to identify new therapeutic strategies related to CIN genes by performing a drug screen, using cells that individually express CIN-associated genes in an inducible manner. We find that the overexpression of targeting protein for Xklp2 (TPX2) enhances sensitivity to the proto-oncogene c-Src (SRC) inhibitor dasatinib due to activation of the Yes-associated protein 1 (YAP) pathway. Furthermore, using breast cancer data from The Cancer Genome Atlas (TCGA) and a cohort of cancer-derived patient samples, we find that both TPX2 overexpression and YAP activation are present in a significant percentage of cancer tumor samples and are associated with poor prognosis; therefore, they are putative biomarkers for selection for dasatinib therapy.

Iron Metabolism and Inflammatory Mediators in Patients with Renal Dysfunction

Chronic kidney disease (CKD) affects around 850 million people worldwide, posing significant challenges in healthcare due to complications like renal anemia, end-stage kidney disease, and cardiovascular diseases. This review focuses on the intricate interplay between iron metabolism, inflammation, and renal dysfunction in CKD. Renal anemia, prevalent in CKD, arises primarily from diminished erythropoietin (EPO) production and iron dysregulation, which worsens with disease progression. Functional and absolute iron deficiencies due to impaired absorption and chronic inflammation are key factors exacerbating erythropoiesis. A notable aspect of CKD is the accumulation of uremic toxins, such as indoxyl sulfate (IS), which hinder iron metabolism and worsen anemia. These toxins directly affect renal EPO synthesis and contribute to renal hypoxia, thus playing a critical role in the pathophysiology of renal anemia. Inflammatory cytokines, especially TNF-α and IL-6, further exacerbate CKD progression and disrupt iron homeostasis, thereby influencing anemia severity. Treatment approaches have evolved to address both iron and EPO deficiencies, with emerging therapies targeting hepcidin and employing hypoxia-inducible factor (HIF) stabilizers showing potential. This review underscores the importance of integrated treatment strategies in CKD, focusing on the complex relationship between iron metabolism, inflammation, and renal dysfunction to improve patient outcomes.

Ferroptosis As Ultimate Target of Cancer Therapy

Significance: The significance of ferroptosis in cancer therapeutics has now been unveiled. Specific ferroptosis inducers are expected as a promising strategy for cancer treatment, especially in cancers with epithelial mesenchymal transition and possibly in cancers with activated Hippo signaling pathways, both of which cause resistance to traditional chemotherapy but tend to show ferroptosis susceptibility. Recent Advances: Ferroptosis is a new form of regulated non-apoptotic cell death, which is characterized by iron-dependent lipid peroxidation, leading eventually to plasma membrane rupture. Its core mechanisms have been elucidated, consisting of a driving force as catalytic Fe(II)-dependent Fenton reaction and an incorporation of polyunsaturated fatty acids to membrane phospholipids via peroxisome-dependent and -independent pathways, and suppressing factors as prevention of lipid peroxidation with glutathione peroxidase 4 and direct membrane repair via coenzyme Q10 and ESCRT-III pathways. Critical Issues: Developments of ferroptosis inducers are in progress by nanotechnology-based drugs or by innovative engineering devices. Especially, low-temperature (non-thermal) plasma is a novel technology at the preclinical stage. The exposure can induce ferroptosis selectively in cancer cells rich in catalytic Fe(II). Future Directions: We also summarize and discuss the recently uncovered responsible molecular mechanisms in association with iron metabolism, ferroptosis and cancer therapeutics. Targeting ferroptosis in addition to the current therapeutic modalities would be important to cure advanced-stage cancer.

Possible Future Avenues for Rheumatoid Arthritis Therapeutics: Hippo Pathway

Rheumatoid arthritis (RA) is a persistent systemic autoimmune disease with the hallmarks of swelling of the joint, joint tenderness, and progressive joint destruction, which may cause synovial inflammation and pannus as a basic pathological change, resulting in joint malformations and serious disorders. At present, the precise etiology and mechanism of pathogenesis of RA are unknown. The imbalance of immune homeostasis is the origin of RA. Hippo pathway is widely expressed in a range of cell lineages and plays a fundamental role in maintaining the immune steady state and may be involved in the pathogenic mechanism of RA. This study reviews the progress of Hippo pathway and its main members in the pathogenesis of RA from three aspects: regulating the maintenance of autoimmune homeostasis, promoting the pathogenicity of synovial fibroblasts and regulating the differentiation of osteoclasts. The study also presents a new way to recognize the pathogenesis of rheumatoid arthritis, which is favorable for finding a new way for treating the rheumatoid arthritis.

Expression of Key Factors of the Hippo Signaling Pathway in Yak (Bos grunniens) Mammary Gland

Simple Summary

The Hippo signaling pathway plays a significant role in regulating the organ development processes of mammals. Our research aimed to investigate the expression and distribution of key members of the Hippo signaling pathway in yak mammary glands during different stages. Using immunohistochemistry, Western blot, and relative quantitative real-time polymerase chain reaction techniques, we found that the protein and mRNA expression levels of MST1, LATS1, YAP1 and TEAD1 in the yak’s mammary gland varies with the growth, lactation, and dry periods. The differential expression in the yak’s mammary gland at different stages strongly suggests that the Hippo signaling pathway plays an important role in regulating the mammary gland development processes under different physiological conditions.

Abstract

Due to its rich nutritional value, yak milk is an important food source in the alpine pastoral areas. However, yaks have a low milk yield. The Hippo pathway participates in cell proliferation and organ development. We aimed to determine the regulatory mechanism of this pathway in yak mammary cells. A greater understanding of how the expression of its essential genes influence the reproductive cycle could lead to improvements in lactation performance. The expression levels of the key genes MST1, LATS1, YAP1, and TEAD1 were detected by quantitative real-time PCR, Western blotting, and immunohistochemistry during the growth, lactation, and dry periods (GP, LP and DP, respectively). The MST1 and LATS1 mRNA and protein expression level was highest during GP and lowest during LP. The YAP1 and TEAD1 mRNA and protein expression level decreased from GP to LP and DP. MST1 and LATS1 were expressed in the cytoplasm whereas YAP1 and TEAD1 were expressed in the nucleus and cytoplasm, respectively. The differential expression of MST1, LATS1, YAP1, and TEAD1 expression in the yak mammary gland during different developmental stages strongly suggests that they play an important role in the regulation of developmental functions under different physiological conditions.

Vitamin B6 Deficiency Promotes Loss of Heterozygosity (LOH) at the Drosophila warts (wts) Locus

The active form of vitamin B6, pyridoxal 5'-phosphate (PLP), is a cofactor for more than 200 enzymes involved in many metabolic pathways. Moreover, PLP has antioxidant properties and quenches the reactive oxygen species (ROS). Accordingly, PLP deficiency causes chromosome aberrations in Drosophila, yeast, and human cells. In this work, we investigated whether PLP depletion can also cause loss of heterozygosity (LOH) of the tumor suppressor warts (wts) in Drosophila. LOH is usually initiated by DNA breakage in heterozygous cells for a tumor suppressor mutation and can contribute to oncogenesis inducing the loss of the wild-type allele. LOH at the wts locus results in epithelial wts homozygous tumors easily detectable on adult fly cuticle. Here, we found that PLP depletion, induced by two PLP inhibitors, promotes LOH of wts locus producing significant frequencies of wts tumors (~7% vs. 2.3%). In addition, we identified the mitotic recombination as a possible mechanism through which PLP deficiency induces LOH. Moreover, LOH of wts locus, induced by PLP inhibitors, was rescued by PLP supplementation. These data further confirm the role of PLP in genome integrity maintenance and indicate that vitamin B6 deficiency may impact on cancer also by promoting LOH.

Hippo signalling in the liver: role in development, regeneration and disease

The Hippo signalling pathway has emerged as a major player in many aspects of liver biology, such as development, cell fate determination, homeostatic function and regeneration from injury. The regulation of Hippo signalling is complex, with activation of the pathway by diverse upstream inputs including signals from cellular adhesion, mechanotransduction and crosstalk with other signalling pathways. Pathological activation of the downstream transcriptional co-activators yes-associated protein 1 (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ, encoded by WWTR1), which are negatively regulated by Hippo signalling, has been implicated in multiple aspects of chronic liver disease, such as the development of liver fibrosis and tumorigenesis. Thus, development of pharmacological inhibitors of YAP-TAZ signalling has been an area of great interest. In this Review, we summarize the diverse roles of Hippo signalling in liver biology and highlight areas where outstanding questions remain to be investigated. Greater understanding of the mechanisms of Hippo signalling in liver function should help facilitate the development of novel therapies for the treatment of liver disease.

Inter-Species Rescue of Mutant Phenotype—The Standard for Genetic Analysis of Human Genetic Disorders in Drosophila melanogaster Model

Drosophila melanogaster (the fruit fly) is arguably a superstar of genetics, an astonishing versatile experimental model which fueled no less than six Nobel prizes in medicine. Nowadays, an evolving research endeavor is to simulate and investigate human genetic diseases in the powerful D. melanogaster platform. Such a translational experimental strategy is expected to allow scientists not only to understand the molecular mechanisms of the respective disorders but also to alleviate or even cure them. In this regard, functional gene orthology should be initially confirmed in vivo by transferring human or vertebrate orthologous transgenes in specific mutant backgrounds of D. melanogaster. If such a transgene rescues, at least partially, the mutant phenotype, then it qualifies as a strong candidate for modeling the respective genetic disorder in the fruit fly. Herein, we review various examples of inter-species rescue of relevant mutant phenotypes of the fruit fly and discuss how these results recommend several human genes as candidates to study and validate genetic variants associated with human diseases. We also consider that a wider implementation of this evolutionist exploratory approach as a standard for the medicine of genetic disorders would allow this particular field of human health to advance at a faster pace.

The Hippo Signaling Pathway in Cancer: A Cell Cycle Perspective

Simple Summary

Cancer is increasingly viewed as a cell cycle disease in that the dysregulation of the cell cycle machinery is a common feature in cancer. The Hippo signaling pathway consists of a core kinase cascade as well as extended regulators, which together control organ size and tissue homeostasis. The aberrant expression of cell cycle regulators and/or Hippo pathway components contributes to cancer development, and for this reason, we specifically focus on delineating the roles of the Hippo pathway in the cell cycle. Improving our understanding of the Hippo pathway from a cell cycle perspective could be used as a powerful weapon in the cancer battlefield.

Abstract

Cell cycle progression is an elaborate process that requires stringent control for normal cellular function. Defects in cell cycle control, however, contribute to genomic instability and have become a characteristic phenomenon in cancers. Over the years, advancement in the understanding of disrupted cell cycle regulation in tumors has led to the development of powerful anti-cancer drugs. Therefore, an in-depth exploration of cell cycle dysregulation in cancers could provide therapeutic avenues for cancer treatment. The Hippo pathway is an evolutionarily conserved regulator network that controls organ size, and its dysregulation is implicated in various types of cancers. Although the role of the Hippo pathway in oncogenesis has been widely investigated, its role in cell cycle regulation has not been comprehensively scrutinized. Here, we specifically focus on delineating the involvement of the Hippo pathway in cell cycle regulation. To that end, we first compare the structural as well as functional conservation of the core Hippo pathway in yeasts, flies, and mammals. Then, we detail the multi-faceted aspects in which the core components of the mammalian Hippo pathway and their regulators affect the cell cycle, particularly with regard to the regulation of E2F activity, the G1 tetraploidy checkpoint, DNA synthesis, DNA damage checkpoint, centrosome dynamics, and mitosis. Finally, we briefly discuss how a collective understanding of cell cycle regulation and the Hippo pathway could be weaponized in combating cancer.

Targeting cardiomyocyte proliferation as a key approach of promoting heart repair after injury

Cardiovascular diseases such as myocardial infarction (MI) is a major contributor to human mortality and morbidity. The mammalian adult heart almost loses its plasticity to appreciably regenerate new cardiomyocytes after injuries, such as MI and heart failure. The neonatal heart exhibits robust proliferative capacity when exposed to varying forms of myocardial damage. The ability of the neonatal heart to repair the injury and prevent pathological left ventricular remodeling leads to preserved or improved cardiac function. Therefore, promoting cardiomyocyte proliferation after injuries to reinitiate the process of cardiomyocyte regeneration, and suppress heart failure and other serious cardiovascular problems have become the primary goal of many researchers. Here, we review recent studies in this field and summarize the factors that act upon the proliferation of cardiomyocytes and cardiac repair after injury and discuss the new possibilities for potential clinical treatment strategies for cardiovascular diseases.

PRAMEF2-mediated dynamic regulation of YAP signaling promotes tumorigenesis

PRAMEF2 is a member of the PRAME multigene family of cancer testis antigens, which serve as prognostic markers for several cancers. However, molecular mechanisms underlying its role in tumorigenesis remain poorly understood. Here, we report that PRAMEF2 is repressed under conditions of altered metabolic homeostasis in a FOXP3-dependent manner. We further demonstrate that PRAMEF2 is a BC-box containing substrate recognition subunit of Cullin 2-based E3 ubiquitin ligase complex. PRAMEF2 mediates polyubiquitylation of LATS1 kinase of the Hippo/YAP pathway, leading to its proteasomal degradation. The site for ubiquitylation was mapped to the conserved Lys860 residue in LATS1. Furthermore, LATS1 degradation promotes enhanced nuclear accumulation of the transcriptional coactivator YAP, resulting in increased expression of proliferative and metastatic genes. Thus, PRAMEF2 promotes malignant phenotype in a YAP-dependent manner. Additionally, elevated PRAMEF2 levels correlate with increased nuclear accumulation of YAP in advanced grades of breast carcinoma. These findings highlight the pivotal role of PRAMEF2 in tumorigenesis and provide mechanistic insight into YAP regulation.

SUMOylation activates large tumour suppressor 1 to maintain the tissue homeostasis during Hippo signalling

Large tumour suppressor (LATS) 1/2, the core kinases of Hippo signalling, are critical for maintaining tissue homeostasis. Here, we investigate the role of SUMOylation in the regulation of LATS activation. High cell density induces the expression of components of the SUMOylation machinery and enhances the SUMOylation and activation of Lats1 but not Lats2, whereas genetic deletion of the SUMOylation E2 ligase, Ubc9, abolishes this Lats1 activation. Moreover, SUMOylation occurs at the K830 (mouse K829) residue to activate LATS1 and depends on the PIAS1/2 E3 ligase. Whereas the K830 deSUMOylation mutation of LATS1 found in the human metastatic prostate cancers eliminates the kinase activity by attenuating the formation of the phospho-MOB1/phospho-LATS1 complex. As a result, the LATS1(K830R) transgene phenocopies Yap transgene to cause the oversized livers in mice, whereas Lats1(K829R) knock-in phenocopies the deletion of Lats1 in causing the reproductive and endocrine defects and ovary tumours in mice. Thus, SUMOylation-mediated LATS1 activation is an integral component of Hippo signalling in the regulation of tissues homeostasis.

NDR/LATS-family protein kinase genes are indispensable for embryogenesis in Arabidopsis

NDR/LATS‐family protein kinases are conserved among eukaryotes. These protein kinases in yeast and animals phosphorylate specific targets and regulate the cell cycle. Arabidopsis thaliana has eight NDR/LATS‐family protein kinase genes (NDR1‐8), of which NDR2, NDR4, and NDR5 are involved in regulating pollen development. However, the functions of the other NDR/LATS‐family protein kinase genes in plants are unclear. Here, we show that three putative phosphorylation sites of an Arabidopsis basic leucine zipper transcription factor, VIP1, correspond to NDR/LATS‐family protein kinase phosphorylation motifs and that two of these three sites are phosphorylated by NDR2, NDR3, or NDR8 in vitro. Expression of NDR1‐8 was detected in various tissues. An NDR4 NDR6 NDR7 NDR8 quadruple mutation caused embryonic lethality These results suggest that different NDR/LATS‐family protein kinases in plants have distinct physiological roles.

Hippo pathway effectors YAP and TAZ and their association with skeletal muscle ageing

Skeletal muscle atrophy commonly occurs during ageing, thus pathways that regulate muscle mass may represent a potential therapeutic avenue for interventions. In this review, we explored the Hippo signalling pathway which plays an essential role in human oncogenesis and the pathway's influence on myogenesis and satellite cell functions, on supporting cells such as fibroblasts, and autophagy. YAP/TAZ was found to regulate both myoblast proliferation and differentiation, albeit with unique roles. Additionally, YAP/TAZ has different functions depending on the expressing cell type, making simple inference of their effects difficult. Studies in cancers have shown that the Hippo pathway influenced the autophagy pathway, although with mixed results. Most of the present researches on YAP/TAZ are focused on its oncogenicity and further studies are needed to translate these findings to physiological ageing. Taken together, the modulation of YAP/TAZ or the Hippo pathway in general may offer potential new strategies for the prevention or treatment of ageing.

YAP1 and its fusion proteins in cancer initiation, progression and therapeutic resistance

YAP1 is a transcriptional co-activator whose activity is controlled by the Hippo signaling pathway. In addition to important functions in normal tissue homeostasis and regeneration, YAP1 has also prominent functions in cancer initiation, aggressiveness, metastasis, and therapy resistance. In this review we are discussing the molecular functions of YAP1 and its roles in cancer, with a focus on the different mechanisms of de-regulation of YAP1 activity in human cancers, including inactivation of upstream Hippo pathway tumor suppressors, regulation by intersecting pathways, miRNAs, and viral oncogenes. We are also discussing new findings on the function and biology of the recently identified family of YAP1 gene fusions, that constitute a new type of activating mutation of YAP1 and that are the likely oncogenic drivers in several subtypes of human cancers. Lastly, we also discuss different strategies of therapeutic inhibition of YAP1 functions.

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.

Regulation and functions of the Hippo pathway in stemness and differentiation

The Hippo pathway plays important roles in organ development, tissue regeneration, and human diseases, such as cancer. In the canonical Hippo pathway, the MST1/2-LATS1/2 kinase cascade phosphorylates and inhibits transcription coactivators Yes-associated protein and transcription coactivator with PDZ-binding motif and thus regulates transcription of genes important for cell proliferation and apoptosis. However, recent studies have depicted a much more complicate picture of the Hippo pathway with many new components and regulatory stimuli involving both chemical and mechanical signals. Furthermore, accumulating evidence indicates that the Hippo pathway also plays important roles in the determination of cell fates, such as self-renewal and differentiation. Here, we review regulations of the Hippo pathway and its functions in stemness and differentiation emphasizing recent discoveries.

Genetic alterations in cell cycle regulation-associated genes may promote primary progression of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are one of the most common mesenchymal tumor types and usually contain KIT or PDGFRA mutations. GISTs with concomitant low- and high-grade components are seen in clinical practice. Herein, we retrospectively analyzed the histological characteristics and immunohistochemical results of 22 GIST cases with concomitant low- and high-grade tumors. Whole-exome sequencing (WES) was performed on ten pairs of high-grade GIST specimens and matched low-grade samples. Differential oncogenes mutated only in high-grade GISTs were identified, which were confirmed by Sanger sequencing. Fluorescence in situ hybridization was employed to detect MYC copy number variation. High-grade GISTs were more likely to have lower CD34 expression and a higher Ki-67 proliferation index compared to the matched low-grade tumors. WES identified 30 differential cancer-associated genes mutated only in high-grade GISTs; Sanger sequencing confirmed ten relevant differential oncogenic mutations in nine genes (MGA, ARID1A, LATS2, MAX, PIK3CA, RB1, RPS6KB2, SDHA, and SETD2). Two patients had MGA mutations, whereas other gene mutations occurred in only one patient. Most of the differential cancer-associated genes are mainly involved in cell cycle control. MYC copy number gain was a common genetic variation. High-grade GISTs revealed more MYC copy number gains than matched low-grade tumors, and low-grade GISTs with coexisting high-grade components showed more MYC copy number gains than pure low-grade GISTs. Moreover, MYC copy number gain was positively correlated with the mitotic index and Ki-67 proliferation index. Alterations in cell cycle regulation-associated genes, such as genetic mutations and MYC copy number gain, may promote primary progression from low-grade GISTs to high-grade tumors by regulating tumor cell proliferation.

MOB1 regulates thymocyte egress and T-cell survival in mice in a YAP1-independent manner

Mammalian STE20-like protein kinase 1/2 (MST1/2) and nuclear Dbf2-related kinase 1/2 (NDR1/2) are core components of Hippo signaling that are also known to be important regulators of lymphocyte trafficking. However, little is understood about the roles of other Hippo pathway molecules in these cells. Here, we present the first analysis of the function of Mps one binder kinase activator-1 (MOB1) in T lymphocytes in vivo. T-cell-specific double knockout (DKO) of MOB1A/B in mice [tMob1 DKO mice] reduces the number of naïve T cells in both the circulation and secondary lymphoid organs, but leads to an accumulation of CD4⁺ CD8^- and CD4^- CD8⁺ single-positive (SP) cells in the thymus. In vitro, naïve MOB1A/B-deficient T cells show increased apoptosis and display impaired trafficking capacity in response to the chemokine CCL19. These defects are linked to suppression of the activation of MST and NDR kinases, but are independent of the downstream transcriptional co-activator Yes-associated protein 1 (YAP1). Thus, MOB1 proteins play an important role in thymic egress and T-cell survival that is mediated by a pathway other than conventional Hippo-YAP1 signaling.

Gap Junction Channels of Innexins and Connexins: Relations and Computational Perspectives

Gap junction (GJ) channels in invertebrates have been used to understand cell-to-cell communication in vertebrates. GJs are a common form of intercellular communication channels which connect the cytoplasm of adjacent cells. Dysregulation and structural alteration of the gap junction-mediated communication have been proven to be associated with a myriad of symptoms and tissue-specific pathologies. Animal models relying on the invertebrate nervous system have exposed a relationship between GJs and the formation of electrical synapses during embryogenesis and adulthood. The modulation of GJs as a therapeutic and clinical tool may eventually provide an alternative for treating tissue formation-related diseases and cell propagation. This review concerns the similarities between Hirudo medicinalis innexins and human connexins from nucleotide and protein sequence level perspectives. It also sets forth evidence of computational techniques applied to the study of proteins, sequences, and molecular dynamics. Furthermore, we propose machine learning techniques as a method that could be used to study protein structure, gap junction inhibition, metabolism, and drug development.

Hippo signaling is intrinsically regulated during cell cycle progression by APC/CCdh1

The Hippo-YAP/TAZ signaling pathway plays a pivotal role in growth control during development and regeneration and its dysregulation is widely implicated in various cancers. To further understand the cellular and molecular mechanisms underlying Hippo signaling regulation, we have found that activities of core Hippo signaling components, large tumor suppressor (LATS) kinases and YAP/TAZ transcription factors, oscillate during mitotic cell cycle. We further identified that the anaphase-promoting complex/cyclosome (APC/C)^Cdh1 E3 ubiquitin ligase complex, which plays a key role governing eukaryotic cell cycle progression, intrinsically regulates Hippo signaling activities. CDH1 recognizes LATS kinases to promote their degradation and, hence, YAP/TAZ regulation by LATS phosphorylation is under cell cycle control. As a result, YAP/TAZ activities peak in G1 phase. Furthermore, we show in Drosophila eye and wing development that Cdh1 is required in vivo to regulate the LATS homolog Warts with a conserved mechanism. Cdh1 reduction increased Warts levels, which resulted in reduction of the eye and wing sizes in a Yorkie dependent manner. Therefore, LATS degradation by APC/C^Cdh1 represents a previously unappreciated and evolutionarily conserved layer of Hippo signaling regulation.

Dysregulation of the Hippo pathway signaling in aging and cancer

Human beings are facing emerging degenerative and cancer diseases, in large part, as a consequence of increased life expectancy. In the near future, researchers will have to put even more effort into fighting these new challenges, one of which will be prevention of cancer while continuing to improve the aging process through this increased life expectancy. In the last few decades, relevance of the Hippo pathway on cancer has become an important study since it is a major regulator of organ size control and proliferation. However, its deregulation can induce tumors throughout the body by regulating cell proliferation, disrupting cell polarity, releasing YAP and TAZ from the Scribble complexes and facilitating survival gene expression via activation of TEAD transcription factors. This pathway is also involved in some of the most important mechanisms that control the aging processes, such as the AMP-activated protein kinase and sirtuin pathways, along with autophagy and oxidative stress response/antioxidant defense. This could be the link between two tightly connected processes that could open a broader range of targeted molecular therapies to fight aging and cancer. Therefore, available knowledge of the processes involved in the Hippo pathway during aging and cancer must necessarily be well understood.

BmHpo mutation induces smaller body size and late stage larval lethality in the silkworm, Bombyx mori

As a core member of the Hippo signaling pathway, Hpo plays a critical role in regulating growth and development. Previous studies reported that loss of function of Hpo results in increased proliferation, reduced apoptosis and induction of tissue overgrowth in Drosophila. In this study, we used CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/Cas9) to study Hpo gene (BmHpo) function in the lepidopteran insect Bombyx mori, known commonly as the silkworm. Sequence analysis of BmHpo revealed an array of deletions in mutants. We found that BmHpo knockout resulted in defects in body size regulation, in developmental defects and pigment accumulation and early death. Our data show that BmHpo is essential for regulation of insect growth and development and that CRISPR/Cas9 technology can serve as a basis for functional analysis of target genes in lepidopteran insects.

Genome editing reveals the function of Yorkie during the embryonic and early larval development in silkworm, Bombyx mori

As a transcriptional coactivator, Yorkie (Yki) is a major downstream target of the Hippo signalling pathway to regulate the organ size during animal development and regeneration. Previous microarray analysis in the silkworm, Bombyx mori, has shown that genes associated with the Hippo pathway were primarily expressed in gonads and imaginal discs. The RNA-interference-mediated silencing of Yki at the early wandering stage delayed B. mori development and ovary maturation, whereas baculovirus-mediated overexpression at the late larval instar facilitated organ growth and accelerated metamorphosis. Here, we employed CRISPR/Cas9-mediated mutagenesis to investigate the function of Yki in B. mori (BmYki) at the embryonic and early larval stages. Knocking out of BmYki led to reduced body size, moulting defects and, eventually, larval lethality. Sequence analysis of CRISPR/Cas9 mutants exhibited an array of deletions in BmYki. As a critical downstream effector of the Hippo kinase cassette, silencing of BmYki at the embryonic stage is indispensable and the consequence is lethal. Given that the Hippo signalling pathway is evolutionarily conserved, Yki has the potential to be a novel molecular target for genetic-based pest management practices.

Dual Role of a C-Terminally Truncated Isoform of Large Tumor Suppressor Kinase 1 in the Regulation of Hippo Signaling and Tissue Growth

The considerable amount of experimental evidence has defined the Hippo pathway as a tumor suppressive pathway and increased expression and/or activity of its oncogenic effectors is frequently observed in cancer. However, clinical studies have failed to attribute cancer development and progression to mutations in the pathway. In explaining this conundrum, we investigated the expression and functions of a C-terminally truncated isoform of large tumor suppressor kinase 1 (LATS1) called short LATS1 (sLATS1) in human cell lines and Drosophila. Intriguingly, through overexpression of sLATS1, we demonstrated that sLATS1 either activates or suppresses the activity of Yes-associated protein (YAP), one of the effectors of the Hippo pathway, in a cell type-specific manner. The activation is mediated through inhibition of full-length LATS1, whereas suppression of YAP is accomplished through sLATS1-YAP interaction. In HEK293T cells, the former mechanism may affect the cellular response more dominantly, whereas in U2OS cells and developing tissues in Drosophila, the latter mechanism may be solely carried out. Finally, to find the clinical relevance of this molecule, we examined the expression of sLATS1 in breast cancer patients. The transcriptome analysis showed that the ratio of sLATS1 to LATS1 was increased in tumor tissues comparing to their adjacent normal tissues.

Decreased expression of LATS1 correlates with astrogliosis after spinal cord injury

Large tumor suppressor kinase 1 (LATS1) is a serine/threonine kinase of the AGC kinase family in mammals and involved in various biological processes, it is a key regulator of cell cycle progression. However, the role of LATS1 in central nervous system trauma is still unknown. In present study, we performed an acute spinal cord injury (SCI) model in adult rats and investigated the dynamic changes of LATS1 expression in the spinal cord. We found that LATS1 protein levels were significantly decreased at day 1 after injury. Meanwhile, double immunofluorescence staining showed these changes were striking in astrocytes, which were largely proliferated after SCI. In vitro, LATS1 overexpression inhibited astrocyte proliferation. Conversely, LATS1 depletion by siRNA promoted cell proliferation in primary astrocyte. Moreover, LATS1 overexpression reduced cyclin D1 expression and increased the expression of p27^kip1. In addition, LATS1 overexpression also promoted yes-associated protein 1 (YAP) phosphorylation. Our data suggested that LATS1 might play an important role in spinal cord injury and suppress astrogliosis through regulating the expression of cyclin D1, p27^kip1 and p-YAP.

The history and regulatory mechanism of the Hippo pathway

How the organ size is adjusted to the proper size during development and how organs know that they reach the original size during regeneration remain long-standing questions. Based on studies using multiple model organisms and approaches for over 20 years, a consensus has been established that the Hippo pathway plays crucial roles in controlling organ size and maintaining tissue homeostasis. Given the significance of these processes, the dysregulation of the Hippo pathway has also implicated various diseases, such as tissue degeneration and cancer. By regulating the downstream transcriptional coactivators YAP and TAZ, the Hippo pathway coordinates cell proliferation and apoptosis in response to a variety of signals including cell contact inhibition, polarity, mechanical sensation and soluble factors. Since the core components and their functions of the Hippo pathway are evolutionarily conserved, this pathway serves as a global regulator of organ size control. Therefore, further investigation of the regulatory mechanisms will provide physiological insights to better understand tissue homeostasis. In this review, the historical developments and current understandings of the regulatory mechanism of Hippo signaling pathway are discussed.

The regulation and function of the Hippo pathway in heart regeneration

Heart failure caused by cardiomyocyte loss and fibrosis is a leading cause of death worldwide. Although current treatments for heart failure such as heart transplantation and left ventricular assist device implantation have obvious value, new approaches are needed. Endogenous adult cardiomyocyte renewal is measurable but inefficient and inadequate in response to extensive acute heart damage. Stimulating self-renewal of endogenous cardiomyocytes holds great promise for heart repair. Uncovering the genetic mechanisms underlying cardiomyocyte renewal is a critical step in developing new approaches to repairing the heart. Recent studies have revealed that the inhibition of the Hippo pathway is sufficient to promote the proliferation of endogenous cardiomyocytes, indicating that the manipulation of the Hippo pathway in the heart may be a promising treatment for heart failure in the future. We summarize recent findings that have shed light on the function of the Hippo pathway in heart regeneration. We also discuss the mechanisms by which Hippo pathway inhibition promotes heart regeneration and how the Hippo pathway responds to different types of injury or stress during the regenerative process. This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration.

FOXP4-AS1 participates in the development and progression of osteosarcoma by downregulating LATS1 via binding to LSD1 and EZH2

Osteosarcoma (OS) is the most common malignant bone tumor in children and adolescents. LncRNA has been confirmed to participate in a variety of cancers. The purpose of this study was to explore the effect of FOXP4-AS1 on the development of osteosarcoma (OS) and its underlying mechanism. FOXP4-AS1 expressions in 60 OS tissues and paracancerous tissues were detected by qRT-PCR (quantitative real-time polymerase chain reaction). We confirmed that FOXP4-AS1 was overexpressed in OS tissues than that of paracancerous tissues. The disease-free survival and overall survival of OS patients were not correlated with age, gender and tumor location, but remarkably correlated with FOXP4-AS1 expression, tumor size and lung metastasis. For in vitro experiments, MG63 cells expressed a higher expression of FOXP4-AS1, whereas U2OS cells expressed a lower expression, which were selected for the following studies. Overexpressed FOXP4-AS1 led to enhanced proliferation, migration and invasion, shortened G0/G1 phase, as well as inhibited cell cycle. Knockdown of FOXP4-AS1 in MG63 cells obtained the opposite results. Furthermore, RIP assay indicated that FOXP4-AS1 could inhibit LATS1 expression by binding to LSD1 and EZH2, so as to participate in OS development. In conclusion, these results revealed that FOXP4-AS1 is overexpressed in OS, and is the independent risk factor in OS prognosis. Upregulated FOXP4-AS1 promotes the proliferation, migration and cell cycle, but inhibits apoptosis of OS cells. Furthermore, FOXP4-AS1 participates in the development and progression of OS by downregulating LATS1 via binding to LSD1 and EZH2.

A Drosophila Tumor Suppressor Gene Prevents Tonic TNF Signaling through Receptor N-Glycosylation

Drosophila tumor suppressor genes have revealed molecular pathways that control tissue growth, but mechanisms that regulate mitogenic signaling are far from understood. Here we report that the Drosophila TSG tumorous imaginal discs (tid), whose phenotypes were previously attributed to mutations in a DnaJ-like chaperone, are in fact driven by the loss of the N-linked glycosylation pathway component ALG3. tid/alg3 imaginal discs display tissue growth and architecture defects that share characteristics of both neoplastic and hyperplastic mutants. Tumorous growth is driven by inhibited Hippo signaling, induced by excess Jun N-terminal kinase (JNK) activity. We show that ectopic JNK activation is caused by aberrant glycosylation of a single protein, the fly tumor necrosis factor (TNF) receptor homolog, which results in increased binding to the continually circulating TNF. Our results suggest that N-linked glycosylation sets the threshold of TNF receptor signaling by modifying ligand-receptor interactions and that cells may alter this modification to respond appropriately to physiological cues.

Loss of Mob1a/b in mice results in chondrodysplasia due to YAP1/TAZ-TEAD-dependent repression of SOX9

Hippo signaling is modulated in response to cell density, external mechanical forces, and rigidity of the extracellular matrix (ECM). The Mps one binder kinase activator (MOB) adaptor proteins are core components of Hippo signaling and influence Yes-associated protein 1 (YAP1) and transcriptional co-activator with PDZ-binding motif (TAZ), which are potent transcriptional regulators. YAP1/TAZ are key contributors to cartilage and bone development but the molecular mechanisms by which the Hippo pathway controls chondrogenesis are largely unknown. Cartilage is rich in ECM and also subject to strong external forces - two upstream factors regulating Hippo signaling. Chondrogenesis and endochondral ossification are tightly controlled by growth factors, morphogens, hormones, and transcriptional factors that engage in crosstalk with Hippo-YAP1/TAZ signaling. Here, we generated tamoxifen-inducible, chondrocyte-specific Mob1a/b-deficient mice and show that hyperactivation of endogenous YAP1/TAZ impairs chondrocyte proliferation and differentiation/maturation, leading to chondrodysplasia. These defects were linked to suppression of SOX9, a master regulator of chondrogenesis, the expression of which is mediated by TEAD transcription factors. Our data indicate that a MOB1-dependent YAP1/TAZ-TEAD complex functions as a transcriptional repressor of SOX9 and thereby negatively regulates chondrogenesis.

Expression of Hippo signaling pathway and Aurora kinase genes in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm resulting from clonal expansion of hematopoietic stem cells positive for the Philadelphia chromosome. The CML pathogenesis is associated with expression of the BCR-ABL1 oncogene, which encodes the Bcr-Abl protein with tyrosine kinase activity, promoting the leukemic cell exacerbated myeloproliferation and resistance to apoptosis. CML patients are usually treated with tyrosine kinase inhibitors (TKI), but some of them acquire resistance or are refractory to TKI. Thus, it is still relevant to elucidate the CML pathogenesis and seek new therapeutic targets, such as the Hippo signaling pathway and cell cycle regulatory genes from the Aurora kinase family. The present study quantified the expression level of genes encoding components of the Hippo signaling pathway (LATS1, LATS2, YAP, and TAZ), AURKA and AURKB in CML patients at different stages of the disease, who were resistant or sensitive to imatinib mesylate therapy, and in healthy individuals. The expression levels of the target genes were correlated with the CML Sokal's prognostic score. The most striking results were the LATS2 and AURKA overexpression in CML patients, the overexpression of TAZ and AURKB in CML patients at advanced phases and TAZ in CML IM-resistant. The development of drugs and/or identification of tumor markers for the Hippo signaling pathway and the Aurora kinase family, either alone or in combination, can optimize CML treatment by enhancing the susceptibility of leukemic cells to apoptosis and leading to a better disease prognosis.

A speculative outlook on embryonic aneuploidy: Can molecular pathways be involved?

The journey of embryonic development starts at oocyte fertilization, which triggers a complex cascade of events and cellular pathways that guide early embryogenesis. Recent technological advances have greatly expanded our knowledge of cleavage-stage embryo development, which is characterized by an increased rate of whole-chromosome losses and gains, mixoploidy, and atypical cleavage morphokinetics. Embryonic aneuploidy significantly contributes to implantation failure, spontaneous miscarriage, stillbirth or congenital birth defects in both natural and assisted human reproduction. Essentially, early embryo development is strongly determined by maternal factors. Owing to considerable limitations associated with human oocyte and embryo research, the use of animal models is inevitable. However, cellular and molecular mechanisms driving the error-prone early stages of development are still poorly described. In this review, we describe known events that lead to aneuploidy in mammalian oocytes and preimplantation embryos. As the processes of oocyte and embryo development are rigorously regulated by multiple signal-transduction pathways, we explore the putative role of signaling pathways in genomic integrity maintenance. Based on the existing evidence from human and animal data, we investigate whether critical early developmental pathways, like Wnt, Hippo and MAPK, together with distinct DNA damage response and DNA repair pathways can be associated with embryo genomic instability, a question that has, so far, remained largely unexplored.

Premature polyadenylation of MAGI3 is associated with diminished N6-methyladenosine in its large internal exon

In cancer, tumor suppressor genes (TSGs) are frequently truncated, causing their encoded products to be non-functional or dominant-negative. We previously showed that premature polyadenylation (pPA) of MAGI3 truncates the gene, switching its functional role from a TSG to a dominant-negative oncogene. Here we report that MAGI3 undergoes pPA at the intron immediately downstream of its large internal exon, which is normally highly modified by N⁶-methyladenosine (m⁶A). In breast cancer cells that upregulate MAGI3^pPA, m⁶A levels in the large internal exon of MAGI3 are significantly reduced compared to cells that do not express MAGI3^pPA. We further find that MAGI3^pPA transcripts are significantly depleted of m⁶A modifications, in contrast to highly m⁶A-modified full-length MAGI3 mRNA. Finally, we analyze public expression data and find that other TSGs, including LATS1 and BRCA1, also undergo intronic pPA following large internal exons, and that m⁶A levels in these exons are reduced in pPA-activated breast cancer cells relative to untransformed mammary cells. Our study suggests that m⁶A may play a role in regulating intronic pPA of MAGI3 and possibly other TSGs, warranting further investigation.

Clinicopathological Significance of Large Tumor Suppressor (LATS) Expression in Gastric Cancer

Purpose

The aims of this study were to evaluate the expression of the large tumor suppressor (LATS) genes LATS1 and LATS2 by immunohistochemical staining of gastric cancer, and to evaluate the clinicopathological significance of LATS expression and its correlation with overall survival (OS).

Materials and Methods

LATS1 and LATS2 expression in a tissue microarray was detected by immunohistochemistry, using 264 gastric cancer specimens surgically resected between July 2006 and December 2009.

Results

Low expression of LATS1 was significantly associated with more advanced American Joint Committee on Cancer (AJCC) stage (P=0.001) and T stage (P=0.032), lymph node (LN) metastasis (P=0.040), perineural invasion (P=0.042), poor histologic grade (P=0.007), and diffuse-type histology by the Lauren classification (P=0.033). Low expression of LATS2 was significantly correlated with older age (≥65, P=0.027), more advanced AJCC stage (P=0.001) and T stage (P=0.001), LN metastasis (P=0.004), perineural invasion (P=0.004), poor histologic grade (P<0.001), and diffuse-type histology by the Lauren classification (P<0.001). Kaplan-Meier survival analysis revealed significantly poor OS rates in the groups with low LATS1 (P=0.037) and LATS2 (P=0.037) expression.

Conclusions

Expression of LATS1 or LATS2 is a significant marker for a good prognosis in patients with gastric cancer.

Stable MOB1 interaction with Hippo/MST is not essential for development and tissue growth control

The Hippo tumor suppressor pathway is essential for development and tissue growth control, encompassing a core cassette consisting of the Hippo (MST1/2), Warts (LATS1/2), and Tricornered (NDR1/2) kinases together with MOB1 as an important signaling adaptor. However, it remains unclear which regulatory interactions between MOB1 and the different Hippo core kinases coordinate development, tissue growth, and tumor suppression. Here, we report the crystal structure of the MOB1/NDR2 complex and define key MOB1 residues mediating MOB1's differential binding to Hippo core kinases, thereby establishing MOB1 variants with selective loss-of-interaction. By studying these variants in human cancer cells and Drosophila, we uncovered that MOB1/Warts binding is essential for tumor suppression, tissue growth control, and development, while stable MOB1/Hippo binding is dispensable and MOB1/Trc binding alone is insufficient. Collectively, we decrypt molecularly, cell biologically, and genetically the importance of the diverse interactions of Hippo core kinases with the pivotal MOB1 signal transducer.The Hippo tumor suppressor pathway is essential for development and tissue growth control. Here the authors employ a multi-disciplinary approach to characterize the interactions of the three Hippo kinases with the signaling adaptor MOB1 and show how they differently affect development, tissue growth and tumor suppression.

Emerging role of Hippo signalling pathway in bladder cancer

Bladder cancer (BC) is one of the most common cancers worldwide with a high progression rate and poor prognosis. The Hippo signalling pathway is a conserved pathway that plays a crucial role in cellular proliferation, differentiation and apoptosis. Furthermore, dysregulation and/or malfunction of the Hippo pathway is common in various human tumours, including BC. In this review, an overview of the Hippo pathway in BC and other cancers is presented. We focus on recent data regarding the Hippo pathway, its network and the regulation of the downstream co-effectors YAP1/TAZ. The core components of the Hippo pathway, which induce BC stemness acquisition, metastasis and chemoresistance, will be emphasized. Additional research on the Hippo pathway will advance our understanding of the mechanism of BC as well as the development and progression of other cancers and may be exploited therapeutically.

Hippo Pathway: An Emerging Regulator of Craniofacial and Dental Development

The evolutionarily conserved Hippo signaling pathway is a vital regulator of organ size that fine-tunes cell proliferation, apoptosis, and differentiation. A number of important studies have revealed critical roles of Hippo signaling and its effectors Yap (Yes-associated protein) and Taz (transcriptional coactivator with PDZ binding motif) in tissue development, homeostasis, and regeneration, as well as in tumorigenesis. In addition, recent studies have shown evidence of crosstalk between the Hippo pathway and other key signaling pathways, such as Wnt signaling, that not only regulates developmental processes but also contributes to disease pathogenesis. In this review, we summarize the major discoveries in the field of Hippo signaling and what has been learned about its regulation and crosstalk with other signaling pathways, with a particular focus on recent findings involving the Hippo-Yap pathway in craniofacial and tooth development. New and exciting studies of the Hippo pathway are anticipated that will significantly improve our understanding of the molecular mechanisms of human craniofacial and tooth development and disease and will ultimately lead to the development of new therapies.

The LATS1 and LATS2 tumor suppressors: beyond the Hippo pathway

Proper cellular functionality and homeostasis are maintained by the convergent integration of various signaling cascades, which enable cells to respond to internal and external changes. The Dbf2-related kinases LATS1 and LATS2 (LATS) have emerged as central regulators of cell fate, by modulating the functions of numerous oncogenic or tumor suppressive effectors, including the canonical Hippo effectors YAP/TAZ, the Aurora mitotic kinase family, estrogen signaling and the tumor suppressive transcription factor p53. While the basic functions of the LATS kinase module are strongly conserved over evolution, the genomic duplication event leading to the emergence of two closely related kinases in higher organisms has increased the complexity of this signaling network. Here, we review the LATS1 and LATS2 intrinsic features as well as their reported cellular activities, emphasizing unique characteristics of each kinase. While differential activities between the two paralogous kinases have been reported, many converge to similar pathways and outcomes. Interestingly, the regulatory networks controlling the mRNA expression pattern of LATS1 and LATS2 differ strongly, and may contribute to the differences in protein binding partners of each kinase and in the subcellular locations in which each kinase exerts its functions.

Molecular Alterations and Expression Dynamics of LATS1 and LATS2 Genes in Non-Small-Cell Lung Carcinoma

Large tumor suppressor (LATS) is an important member of the Hippo pathway which can regulate organ size and cell proliferation. However, very little is known about the expression and clinical significance of LATS in lung cancer especially from this part of the world. We elucidated the frequency of LATS1 &LATS2 promoter hypermethylation (by methylation-specific PCR) and expression (by real-time PCR) in sixty nine (n = 69) Non-Small Cell Lung Cancer (NSCLC) patients and their corresponding normal lung tissue samples. We found promoter hypermethylation frequencies of LATS1 & LATS1to be 66.66% (46/69) and 71% (49/69) in NSCLC tissues. Decreased LATS1 & LATS2 mRNA expression was found in 55% and 66.66% of NSCLC patients. The LATS1 mRNA expression was significantly higher in normal lung tissues. Also, the mRNA levels of LATS1 and LATS2 NSCLC tissues with hypermethylation were significantly lower. Multivariable analysis confirmed that LATS1 under expression increased the hazard of death after adjusting for other clinicopathological factors. Importantly, the loss of LATS1 mRNA expression was associated with overall short survival. LATS1 is an independent prognostic factor and may play an important role in NSCLC progression and may serve as a novel therapeutic target of NSCLC.

LATS1 suppresses proliferation and invasion of cervical cancer

Loss of large tumor suppressor kinase 1 (LATS1)Y has been implicated in numerous types of human cancer. However, its involvement in human cervical cancer remains to be elucidated. The present study aimed to investigate the clinical significance and biological characteristics of LATS1 in human cervical cancer. The present study investigated the protein expression levels of LATS1 in tissues from 80 cases of cervical cancer using immunohistochemistry and demonstrated that LATS1 was downregulated in 45% (36/80) of cervical cancers. Transfection of LATS1 was performed in the SiHa cell line and LATS1 siRNA knockdown was performed in the Caski cell line. MTT assay and Matrigel invasion assay indicated that LATS1 overexpression inhibited cell proliferation and invasion. LATS1 overexpression upregulated p27 expression, and downregulated the expression of cyclin E and matrix metalloproteinase 9. In addition, LATS1 overexpression stimulated yes-associated protein 1 (YAP) phosphorylation. Depletion of LATS1 in Caski cells resulted in the opposite effects. The current study demonstrated that LATS1 was downregulated in cervical cancer and may suppress cell growth and invasion through regulating the expression of cyclin E, p27, MMP9 and YAP.

The Hippo pathway regulates human megakaryocytic differentiation

The Hippo pathway is involved in several biological processes in both flies and mammals. Recent studies have shown that the Hippo pathway regulates Drosophila's haematopoiesis; however, understanding of its role in mammalian haematopoiesis is still limited. In flies, deletion of the Hippo component gene, Warts, affects crystal cell differentiation. We explored the role of the Hippo pathway in human haematopoiesis focusing on megakaryopoiesis. To investigate the role of LATS1/2 (a mammalian homolog of Warts) in human megakaryoblastic cell differentiation and platelet formation, megakaryoblastic cell (MEG-01) line was used as a model to gain insight into mechanism of the Hippo pathway in mammalian megakaryopoiesis. Effect of LATS1/2 on megakaryoblastic cell differentiation and platelet production were determined by functional changes. We found that depletion of LATS1/2 resulted in an increase of CD41⁺ megakaryocytes with impaired platelet biogenesis. Our study shows that the Hippo signalling pathway plays a crucial role in human megakaryoblastic cell differentiation and thrombopoiesis.

The Hippo Pathway Targets Rae1 to Regulate Mitosis and Organ Size and to Feed Back to Regulate Upstream Components Merlin, Hippo, and Warts

Hippo signaling acts as a master regulatory pathway controlling growth, proliferation, and apoptosis and also ensures that variations in proliferation do not alter organ size. How the pathway coordinates restricting proliferation with organ size control remains a major unanswered question. Here we identify Rae1 as a highly-conserved target of the Hippo Pathway integrating proliferation and organ size. Genetic and biochemical studies in Drosophila cells and tissues and in mammalian cells indicate that Hippo signaling promotes Rae1 degradation downstream of Warts/Lats. In proliferating cells, Rae1 loss restricts cyclin B levels and organ size while Rae1 over-expression increases cyclin B levels and organ size, similar to Hippo Pathway over-activation or loss-of-function, respectively. Importantly, Rae1 regulation by the Hippo Pathway is crucial for its regulation of cyclin B and organ size; reducing Rae1 blocks cyclin B accumulation and suppresses overgrowth caused by Hippo Pathway loss. Surprisingly, in addition to suppressing overgrowth, reducing Rae1 also compromises survival of epithelial tissue overgrowing due to loss of Hippo signaling leading to a tissue “synthetic lethality” phenotype. Excitingly, Rae1 plays a highly conserved role to reduce the levels and activity of the Yki/YAP oncogene. Rae1 increases activation of the core kinases Hippo and Warts and plays a post-transcriptional role to increase the protein levels of the Merlin, Hippo, and Warts components of the pathway; therefore, in addition to Rae1 coordinating organ size regulation with proliferative control, we propose that Rae1 also acts in a feedback circuit to regulate pathway homeostasis.

Exquisite control of organ size is critical during animal development and its loss results in pathological conditions. The Hippo Tumor Suppressor Pathway coordinates regulation of proliferation, growth, apoptosis, and autophagy to determine and maintain precise control of organ size. However, the genes responsible for Hippo-mediated regulation of mitosis or coordination of proliferation within organ size control have evaded characterization. Here, we describe Rae1, an essential WD-repeat containing protein, as a new organ size regulator. By genetic analysis, we show that Rae1 acts downstream of the Hippo Pathway to regulate mitotic cyclins and organ size. In contexts where organ size control is lost by compromised Hippo signaling, we show that there is a requirement for Rae1 that is distinct from the requriement for Yki: reducing Yki levels causes suppression of overgrowth, while reducing Rae1 levels dramatically compromises the survival of Hippo-deficient tissue. Lastly, our studies of Rae1 uncovered a potential post-transcriptional feedback loop that reinforces Yorkie-mediated transcriptional feedback for the Hippo Pathway.

Evaluation of mutagenic, recombinogenic and carcinogenic potential of (+)-usnic acid in somatic cells of Drosophila melanogaster

The main of this study was to evaluate the mutagenic and carcinogenic potential of (+) - usnic acid (UA), using Somatic Mutation and Recombination Test (SMART) and the test for detecting epithelial tumor clones (wts) in Drosophila melanogaster. Larvae from 72 ± 4 h from Drosophila were fed with UA (5.0, 10.0 or 20.0 mM); urethane (10.0 mM) (positive control); and solvent (Milli-Q water, 1% Tween-80 and 3% ethanol) (negative control). ST cross produced increase in total mutant spots in the individuals treated with 5.0, 10.0 or 20.0 mM of UA. HB cross produced spot frequencies in the concentration of 5.0 mM that were higher than the frequency for the same concentration in the ST cross. In the highest concentrations the result was negative, which means that the difference observed can be attributed, in part, to the high levels of P450, suggesting that increasing the metabolic capacity maximized the toxic effect of these doses. In the evaluation of carcinogenesis using the wts test, the results obtained for the same concentrations of UA show a positive result for the presence of tumors when compared to the negative control. We conclude that UA has recombinogenic, mutagenic and carcinogenic effects on somatic cells in D. melanogaster.

Fat/Dachsous Signaling Promotes Drosophila Wing Growth by Regulating the Conformational State of the NDR Kinase Warts

Nuclear Dbf2-related (NDR) kinases play a central role in limiting growth in most animals. Signals that promote growth do so in part by suppressing the activation of NDR kinases by STE20/Hippo kinases. Here, we identify another mechanism for downregulating NDR kinase activity. Specifically, we show that activity of the Drosophila NDR kinase Warts in the developing wing depends on its transition from an inactive, "closed" conformation to a potentially active, "open" conformation mediated by Mats, a conserved Mps1-binder (Mob) protein. Further, we show that signaling interactions between the protocadherins Fat and Dachsous, organized by the morphogens Wingless and Decapentaplegic, suppress Warts by acting via the atypical myosin Dachs to inhibit or reverse this transition. The regulation of Warts conformation by Mats, Fat/Dachsous signaling, and Dachs appears independent of Warts phosphorylation by Hippo kinase, establishing a precedent for the control of NDR kinases, and hence growth, by distinct allosteric and phosphorylation mechanisms.

Mechanisms of Hippo pathway regulation

In this review, Meng et al. focus on recent developments in our understanding of the molecular actions of the core Hippo kinase cascade and discuss key open questions in Hippo pathway regulation and function.

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.