Rho1 regulates apoptosis via activation of the JNK signaling pathway at the plasma membrane

Drosophila as a Model Organism to Study Basic Mechanisms of Longevity

The spatio-temporal regulation of gene expression determines the fate and function of various cells and tissues and, as a consequence, the correct development and functioning of complex organisms. Certain mechanisms of gene activity regulation provide adequate cell responses to changes in environmental factors. Aside from gene expression disorders that lead to various pathologies, alterations of expression of particular genes were shown to significantly decrease or increase the lifespan in a wide range of organisms from yeast to human. Drosophila fruit fly is an ideal model system to explore mechanisms of longevity and aging due to low cost, easy handling and maintenance, large number of progeny per adult, short life cycle and lifespan, relatively low number of paralogous genes, high evolutionary conservation of epigenetic mechanisms and signalling pathways, and availability of a wide range of tools to modulate gene expression in vivo. Here, we focus on the organization of the evolutionarily conserved signaling pathways whose components significantly influence the aging process and on the interconnections of these pathways with gene expression regulation.

PI3Kβ-regulated β-catenin mediates EZH2 removal from promoters controlling primed human ESC stemness and primitive streak gene expression

The mechanism governing the transition of human embryonic stem cells (hESCs) toward differentiated cells is only partially understood. To explore this transition, the activity and expression of the ubiquitous phosphatidylinositol 3-kinase (PI3Kα and PI3Kβ) were modulated in primed hESCs. The study reports a pathway that dismantles the restraint imposed by the EZH2 polycomb repressor on an essential stemness gene, NODAL, and on transcription factors required to trigger primitive streak formation. The primitive streak is the site where gastrulation begins to give rise to the three embryonic cell layers from which all human tissues derive. The pathway involves a PI3Kβ non-catalytic action that controls nuclear/active RAC1 levels, activation of JNK (Jun N-terminal kinase) and nuclear β-catenin accumulation. β-Catenin deposition at promoters triggers release of the EZH2 repressor, permitting stemness maintenance (through control of NODAL) and correct differentiation by allowing primitive streak master gene expression. PI3Kβ epigenetic control of EZH2/β-catenin might be modulated to direct stem cell differentiation.

•

PI3Kβ directs epigenetic control of stemness and primitive streak (PS) essential genes

•

PI3Kβ directs RAC1/JNK/β-catenin activation and induces EZH2 promoter displacement

•

β-Catenin/EZH2 control NODAL, a gene essential for stemness and the master PS genes

•

PI3Kβ/PI3K activities cooperate at stemness; PI3Kβ directs PS gene expression

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

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

Toll-7 promotes tumour growth and invasion in Drosophila

Objectives

Drosophila melanogaster has become an excellent model organism to explore the genetic mechanisms underlying tumour progression. Here, by using well‐established Drosophila tumour models, we identified Toll‐7 as a novel regulator of tumour growth and invasion.

Materials and methods

Transgenic flies and genetic epistasis analysis were used. All flies were raised on a standard cornmeal and agar medium at 25°C unless otherwise indicated. Immunostaining and RT‐qPCR were performed by standard procedures. Images were taken by OLYMPUS BX51 microscope and Zeiss LSM 880 confocal microscope. Adobe Photoshop 2020 and Zeiss Zen were used to analyse the images. All results were presented in Scatter plots or Column bar graphs created by GraphPad Prism 8.0.

Results

Loss of Toll‐7 suppresses Ras^V12/lgl^−/−‐induced tumour growth and invasion, as well as cell polarity disruption‐induced invasive cell migration, whereas expression of a constitutively active allele of Toll‐7 is sufficient to promote tumorous growth and cell migration. In addition, the Egr‐JNK signalling is necessary and sufficient for Toll‐7‐induced invasive cell migration. Mechanistically, Toll‐7 facilitates the endocytosis of Egr, which is known to activate JNK in the early endosomes. Moreover, Toll‐7 activates the EGFR‐Ras signalling, which cooperates with the Egr‐JNK signalling to promote Yki‐mediated cell proliferation and tissue overgrowth. Finally, Toll‐7 is necessary and sufficient for the proper maintenance of EGFR protein level.

Conclusions

Our findings characterized Toll‐7 as a proto‐oncogene that promotes tumour growth and invasion in Drosophila, which shed light on the pro‐tumour function of mammalian Toll‐like receptors (TLRs).

The Hh pathway promotes cell apoptosis through Ci-Rdx-Diap1 axis

Apoptosis is a strictly coordinated process to eliminate superfluous or damaged cells, and its deregulation leads to birth defects and various human diseases. The regulatory mechanism underlying apoptosis still remains incompletely understood. To identify novel components in apoptosis, we carry out a modifier screen and find that the Hh pathway aggravates Hid-induced apoptosis. In addition, we reveal that the Hh pathway triggers apoptosis through its transcriptional target gene rdx, which encodes an E3 ubiquitin ligase. Rdx physically binds Diap1 to promote its K63-linked polyubiquitination, culminating in attenuating Diap1-Dronc interaction without affecting Diap1 stability. Taken together, our findings unexpectedly uncover the oncogenic Hh pathway is able to promote apoptosis through Ci-Rdx-Diap1 module, raising a concern to choose Hh pathway inhibitors as anti-tumor drugs.

Drosophila models of metastasis

An important goal in the fight against cancer is to understand how tumors become invasive and metastatic. A crucial early step in metastasis is thought to be the epithelial mesenchymal transition (EMT), the process in which epithelial cells transition into a more migratory and invasive, mesenchymal state. Since the genetic regulatory networks driving EMT in tumors derive from those used in development, analysis of EMTs in genetic model organisms such as the vinegar fly, Drosophila melanogaster, can provide great insight into cancer. In this review I highlight the many ways in which studies in the fly are shedding light on cancer metastasis. The review covers both normal developmental events in which epithelial cells become migratory, as well as induced events, whereby normal epithelial cells become metastatic due to genetic manipulations. The ability to make such precise genetic perturbations in the context of a normal, in vivo environment, complete with a working innate immune system, is making the fly increasingly important in understanding metastasis.

HIPK3 Mediates Inflammatory Cytokines and Oxidative Stress Markers in Monocytes in a Rat Model of Sepsis Through the JNK/c-Jun Signaling Pathway

Sepsis is a fetal immunological disorder and its complication worsens in the patients with hemodialysis which may increase the risk of death. In the present study, we aimed to investigate the effect of homeodomain-interacting protein kinase 3 (HIPK3) on inflammatory factors and oxidative stress markers in monocytes of rats with sepsis by regulating the c-Jun amino-terminal kinase (JNK)/c-Jun signaling pathway. A rat model of sepsis was initially established using cecal ligation and puncture (CLP) and was further identified by enlarged spleen tissues, inflammation, and oxidative stress. Monocytes were isolated from rats with CLP-induced sepsis. HIPK3 was observed to be downregulated while JUN was upregulated in monocytes from rats with CLP-induced sepsis. Furthermore, isolated monocytes were transduced with lentiviral vectors expressing HIPK3 or shRNA against HIPK3 to explore the effect of HIPK3 on viability and apoptosis of monocytes as well as inflammatory factors and oxidative stress markers. The obtained data exhibited that overexpression of HIPK3 or inhibition of the JNK signaling pathway enhanced proliferation, reduced apoptosis of monocytes, alleviated inflammation, and oxidative stress injury. Consistently, our results may provide evidence that HIPK3 could inhibit the JNK/c-Jun signaling pathway, thereby potentially retarding the progression of sepsis.

Drosophila jumu modulates apoptosis via a JNK-dependent pathway and is required for other processes in wing development

Previous studies in several model organisms have revealed that members of the Forkhead (Fkh) transcription factor family have multiple functions. Drosophila Jumeau (Jumu), a member of this family, participates in cardiogenesis, hematopoiesis and immune system homeostasis. Here, we show that loss of jumu function positively regulates or triggers apoptosis via a JNK-dependent pathway in wing development. jumu mutants showed reduced wing size and increased apoptosis. Moreover, we observed a loss of the anterior cross vein (ACV) phenotype that was similar to that observed in wings in which JNK signaling has been ectopically activated. The JNK signaling markers puckered (puc) and p-JNK were also significantly increased in the wing discs of jumu mutants. In addition, apoptosis induced by the loss of jumu was rescued by knocking down JNK, indicating a role for JNK in reducing jumu-induced apoptosis. Jumu could also control wing margin development via the positive regulation of cut expression, and the observed wing margin defect did not result from a loss of jumu-induced apoptosis. Further, jumu deficiency in the pupal wing could induce multiple wing hairs via a Rho1-mediated planar cell polarity pathway, but abnormal Rho1 expression was not why jumu loss induced apoptosis via a JNK-dependent pathway in wing discs.

Gilgamesh (Gish)/CK1γ regulates tissue homeostasis and aging in adult Drosophila midgut

Adult tissues and organs rely on resident stem cells to generate new cells that replenish damaged cells. To maintain homeostasis, stem cell activity needs to be tightly controlled throughout the adult life. Here, we show that the membrane-associated kinase Gilgamesh (Gish)/CK1γ maintains Drosophila adult midgut homeostasis by restricting JNK pathway activity and that Gish is essential for intestinal stem cell (ISC) maintenance under stress conditions. Inactivation of Gish resulted in aberrant JNK pathway activation and excessive production of multiple cytokines and growth factors that drive ISC overproliferation. Mechanistically, Gish restricts JNK activation by phosphorylating and destabilizing a small GTPase, Rho1. Interestingly, we find that Gish expression is down-regulated in aging guts and that increasing Gish activity in aging guts can restore tissue homeostasis. Hence, our study identifies Gish/CK1γ as a novel regulator of Rho1 and gatekeeper of tissue homeostasis whose activity is compromised in aging guts.

Two-Faced: Roles of JNK Signalling During Tumourigenesis in the Drosophila Model

The highly conserved c-Jun N-terminal Kinase (JNK) signalling pathway has many functions, regulating a diversity of processes: from cell movement during embryogenesis to the stress response of cells after environmental insults. Studies modelling cancer using the vinegar fly, Drosophila melanogaster, have identified both pro- and anti-tumourigenic roles for JNK signalling, depending on context. As a tumour suppressor, JNK signalling commonly is activated by conserved Tumour Necrosis Factor (TNF) signalling, which promotes the caspase-mediated death of tumourigenic cells. JNK pathway activation can also occur via actin cytoskeleton alterations, and after cellular damage inflicted by reactive oxygen species (ROS). Additionally, JNK signalling frequently acts in concert with Salvador-Warts-Hippo (SWH) signalling – either upstream of or parallel to this potent growth-suppressing pathway. As a tumour promoter, JNK signalling is co-opted by cells expressing activated Ras-MAPK signalling (among other pathways), and used to drive cell morphological changes, induce invasive behaviours, block differentiation, and enable persistent cell proliferation. Furthermore, JNK is capable of non-autonomous influences within tumour microenvironments by effecting the transcription of various cell growth- and proliferation-promoting molecules. In this review, we discuss these aspects of JNK signalling in Drosophila tumourigenesis models, and highlight recent publications that have expanded our knowledge of this important and versatile pathway.

Drosophila ELYS regulates Dorsal dynamics during development

Embryonic large molecule derived from yolk sac (ELYS) is a constituent protein of nuclear pores. It initiates assembly of nuclear pore complexes into functional nuclear pores toward the end of mitosis. Using cellular, molecular, and genetic tools, including fluorescence and Electron microscopy, quantitative PCR, and RNAi-mediated depletion, we report here that the ELYS ortholog (dElys) plays critical roles during Drosophila development. dElys localized to the nuclear rim in interphase cells, but during mitosis it was absent from kinetochores and enveloped chromatin. We observed that RNAi-mediated dElys depletion leads to aberrant development and, at the cellular level, to defects in the nuclear pore and nuclear lamina assembly. Further genetic analyses indicated that dElys depletion re-activates the Dorsal (NF-κB) pathway during late larval stages. Re-activated Dorsal caused untimely expression of the Dorsal target genes in the post-embryonic stages. We also demonstrate that activated Dorsal triggers apoptosis during later developmental stages by up-regulating the pro-apoptotic genes reaper and hid The apoptosis induced by Reaper and Hid was probably the underlying cause for developmental abnormalities observed upon dElys depletion. Moreover, we noted that dElys has conserved structural features, but contains a noncanonical AT-hook-like motif through which it strongly binds to DNA. Together, our results uncover a novel epistatic interaction that regulates Dorsal dynamics by dElys during development.

Role of Notch Signaling in Leg Development in Drosophila melanogaster

Notch pathway plays diverse and fundamental roles during animal development. One of the most relevant, which arises directly from its unique mode of activation, is the specification of cell fates and tissue boundaries. The development of the leg of Drosophila melanogaster is a fine example of this Notch function, as it is required to specify the fate of the cells that will eventually form the leg joints, the flexible structures that separate the different segments of the adult leg. Notch activity is accurately activated and maintained at the distal end of each segment in response to the proximo-distal patterning gene network of the developing leg. Region-specific downstream targets of Notch in turn regulate the formation of the different types of joints. We discuss recent findings that shed light on the molecular and cellular mechanisms that are ultimately governed by Notch to achieve epithelial fold and joint morphogenesis. Finally, we briefly summarize the role that Notch plays in inducing the nonautonomous growth of the leg. Overall, this book chapter aims to highlight leg development as a useful model to study how patterning information is translated into specific cell behaviors that shape the final form of an adult organ.

Endoplasmic reticulum stress-induced cellular dysfunction and cell death in insulin-producing cells results in diabetes-like phenotypes in Drosophila

The destruction of pancreatic β cells leads to reduced insulin secretion and eventually causes diabetes. Various types of cellular stress are thought to be involved in destruction and/or malfunction of these cells. We show that endoplasmic reticulum (ER) stress accumulation in insulin-producing cells (IPCs) generated diabetes-like phenotypes in Drosophila To promote the accumulation of extra ER stress, we induced a dominant-negative form of a Drosophila ER chaperone protein (Hsc70-3DN) and demonstrate that it causes the unfolded-protein response (UPR) in various tissues. The numbers of IPCs decreased owing to apoptosis induction mediated by caspases. The apoptosis was driven by activation of Dronc, and subsequently by Drice and Dcp-1. Accordingly, the relative mRNA-expression levels of Drosophila insulin-like peptides significantly decreased. Consistent with these results, we demonstrate that glucose levels in larval haemolymph were significantly higher than those of controls. Accumulation of ER stress induced by continuous Hsc70-3DN expression in IPCs resulted in the production of undersized flies. Ectopic expression of Hsc70-3DN can induce more efficient ER stress responses and more severe phenotypes. We propose that ER stress is responsible for IPC loss and dysfunction, which results in diabetes-related pathogenesis in this Drosophila diabetes model. Moreover, inhibiting apoptosis partially prevents the ER stress-induced diabetes-like phenotypes.

Role of α-Catenin and its mechanosensing properties in regulating Hippo/YAP-dependent tissue growth

α-catenin is a key protein of adherens junctions (AJs) with mechanosensory properties. It also acts as a tumor suppressor that limits tissue growth. Here we analyzed the function of Drosophila α-Catenin (α-Cat) in growth regulation of the wing epithelium. We found that different α-Cat levels led to a differential activation of Hippo/Yorkie or JNK signaling causing tissue overgrowth or degeneration, respectively. α-Cat can modulate Yorkie-dependent tissue growth through recruitment of Ajuba, a negative regulator of Hippo signaling to AJs but also through a mechanism independent of Ajuba recruitment to AJs. Both mechanosensory regions of α-Cat, the M region and the actin-binding domain (ABD), contribute to growth regulation. Whereas M is dispensable for α-Cat function in the wing, individual M domains (M1, M2, M3) have opposing effects on growth regulation. In particular, M1 limits Ajuba recruitment. Loss of M1 causes Ajuba hyper-recruitment to AJs, promoting tissue-tension independent overgrowth. Although M1 binds Vinculin, Vinculin is not responsible for this effect. Moreover, disruption of mechanosensing of the α-Cat ABD affects tissue growth, with enhanced actin interactions stabilizing junctions and leading to tissue overgrowth. Together, our findings indicate that α-Cat acts through multiple mechanisms to control tissue growth, including regulation of AJ stability, mechanosensitive Ajuba recruitment, and dynamic direct F-actin interactions.

We explore the regulation of tissue and organ size which is an important consideration in normal development and health. During development, tissues reach specific sizes in proportion to the rest of the body. Uncontrolled growth can lead to malformations or promote tumor growth. Recent findings have emphasized an important role for mechanical cues in the regulation of tissue growth. Mechanical signals can, for example, arise from cytoskeletal contraction that increases tension, or from compression due to proliferation and a resulting increase in cell density that would lower tension. Mechanosensory molecules that are sensitive to changes in tissue tension can convert mechanical cues into biochemical signals that enhance or slow proliferation or cell death to adjust overall tissue size. One such mechanosensory molecule is α-Catenin which is a key component of cell adhesion structures that physically link cells together and couples these structures to the cytoskeleton within cells. We clarify several molecular parameters of how α-Catenin regulates signalling pathways that control cell proliferation and cell death.

Reproduction disrupts stem cell homeostasis in testes of aged male Drosophila via an induced microenvironment

Stem cells rely on instructive cues from their environment. Alterations in microenvironments might contribute to tissue dysfunction and disease pathogenesis. Germline stem cells (GSCs) and cyst stem cells (CySC) in Drosophila testes are normally maintained in the apical area by the testicular hub. In this study, we found that reproduction leads to accumulation of early differentiating daughters of CySCs and GSCs in the testes of aged male flies, due to hyperactivation of Jun-N-terminal kinase (JNK) signaling to maintain self-renewal gene expression in the differentiating cyst cells. JNK activity is normally required to maintain CySCs in the apical niche. A muscle sheath surrounds the Drosophila testis to maintain its long coiled structure. Importantly, reproduction triggers accumulation of the tumor necrosis factor (TNF) Eiger in the testis muscle to activate JNK signaling via the TNF receptor Grindelwald in the cyst cells. Reducing Eiger activity in the testis muscle sheath suppressed reproduction-induced differentiation defects, but had little effect on testis homeostasis of unmated males. Our results reveal that reproduction in males provokes a dramatic shift in the testicular microenvironment, which impairs tissue homeostasis and spermatogenesis in the testes.

Proper differentiation of stem cell progeny is necessary for preservation of tissue homeostasis. In Drosophila testes, somatic cyst cells derived from the cyst stem cells (CySCs) control the differentiation of the neighboring germ cells. Disruption of CySC daughter cyst cell differentiation leads to failure in sperm production. Interestingly, we found that reproduction triggers hyperactivation of Jun-N-terminal kinase (JNK) signaling to sustain CySC self-renewal gene expression in differentiating cyst cells, leading to accumulation of immature cyst cell and germ cells at the expense of mature cells in the testes of aged males. Endogenous JNK signaling is also required for CySC maintenance. Moreover, we found that the JNK signaling is hyperactivated via reproduction-induced accumulation of tumor necrosis factor (TNF) in testicular smooth muscle that surrounds the testis to support its long coiled structure. The reproduction-induced phenotypes were only observed in the testes of aged and mated males, but not in testes form young mated males or aged unmated males, indicating that it is a combined effect of reproduction and aging. Our results reveal that reproduction impedes sperm production in aged males, and identify testicular muscle as an inducible signaling center for spermatogenesis in Drosophila.

JNK signaling coordinates with ecdysone signaling to promote pruning of Drosophila sensory neuron dendrites

Developmental pruning of axons and dendrites is crucial for the formation of precise neuronal connections, but the mechanisms underlying developmental pruning are not fully understood. Here, we have investigated the function of JNK signaling in dendrite pruning using Drosophila class IV dendritic arborization (c4da) neurons as a model. We find that loss of JNK or its canonical downstream effectors Jun or Fos led to dendrite-pruning defects in c4da neurons. Interestingly, our data show that JNK activity in c4da neurons remains constant from larval to pupal stages but the expression of Fos is specifically activated by ecdysone receptor B1 (EcRB1) at early pupal stages, suggesting that ecdysone signaling provides temporal control of the regulation of dendrite pruning by JNK signaling. Thus, our work not only identifies a novel pathway involved in dendrite pruning and a new downstream target of EcRB1 in c4da neurons, but also reveals that JNK and Ecdysone signaling coordinate to promote dendrite pruning.

The transcription factor Dysfusion promotes fold and joint morphogenesis through regulation of Rho1

The mechanisms that control tissue patterning and cell behavior are extensively studied separately, but much less is known about how these two processes are coordinated. Here we show that the Drosophila transcription factor Dysfusion (Dysf) directs leg epithelial folding and joint formation through the regulation of Rho1 activity. We found that Dysf-induced Rho1 activity promotes apical constriction specifically in folding epithelial cells. Here we show that downregulation of Rho1 or its downstream effectors cause defects in fold and joint formation. In addition, Rho1 and its effectors are sufficient to induce the formation of epithelial folds when misexpressed in a flat epithelium. Furthermore, as apoptotic cells can actively control tissue remodeling, we analyzed the role of cell death in the formation of tarsal folds and its relation to Rho1 activity. Surprisingly, we found no defects in this process when apoptosis is inhibited. Our results highlight the coordination between a patterning transcription factor and the cellular processes that cause the cell shape changes necessary to sculpt a flat epithelium into a three dimensional structure.

Epithelial morphogenesis drives the formation of organs and the acquisition of body shape. Changes in cell behavior such as cell proliferation, cell shape or apoptosis contribute to the remodeling of the epithelia from a simple layer to a three dimensional structure. These changes have to be precisely regulated by an underlying patterning network to control the final shape of an organ. However, how these two processes are coordinated is mostly unknown. In this work we use the formation of the fly leg joints as a model to study how Dysfusion (Dysf), a patterning transcription factor, regulates the cellular mechanisms that form the folds in the leg discs epithelium. We have found that dysf modulates the localization and activity of Rho1, a key regulator of the acto-myosin cytoskeleton, to drive cell apical constriction and epithelial folding in the leg disc. Furthermore, in this work we provide proof of the direct requirements of Rho1 and its downstream effectors in fold and joint formation. We conclude that Dysf-regulated Rho1 activity controls the cell shape changes that sculpt leg joints.

Blockade of ITGA2 Induces Apoptosis and Inhibits Cell Migration in Gastric Cancer

Background

Gastric cancer is currently the fourth leading cause of cancer-related death worldwide. Gastric cancer is often diagnosed at advanced stages and the outcome of the treatment is often poor. Therefore, identifying new therapeutic targets for this cancer is urgently needed. Integrin alpha 2 (ITGA2) subunit and the beta 1 subunit form a heterodimer for a transmembrane receptor for extracellular matrix, is an important molecule involved in tumor cell proliferation, survival and migration. Integrin α2β1 is over-expressed on a variety of cancer cells, but is low or absent in most normal organs and resting endothelial cells.

Results

In this report, we assessed the ITGA2 as the potential therapeutic target with the bioinformatics tools from the TCGA dataset in which composed of 375 gastric cancer tissues and 32 gastric normal tissues. According to the information from the Cancer Cell Line Encyclopedia (CCLE) database, the AGS cell line with ITGA2 high expression and the SUN-1 cell line with low expression were chosen for the further investigation. Interestingly, the anti-ITGA2 antibody (at 3 μg/ml) inhibited approximately 50% survival of the AGS cells (over-expressed ITGA2), but had no effect in SNU-1 cells (ITGA2 negative). The extents of antibody-mediated cancer inhibition positively correlated with the expression levels of the ITGA2. We further showed that the anti-ITGA2 antibody induced apoptosis by up-regulating the RhoA-p38 MAPK signaling to promote the expressions of Bim, Apaf-1 and Caspase-9, whereas the expressions of Ras and Bax/Bcl-2 were not affected. Moreover, blocking ITGA2 by the specific antibody at lower doses also inhibited cell migration of gastric cancer cells. Blockade of ITGA2 by a specific antibody down-regulated the expression of N-WASP, PAK and LIMK to impede actin organization and cell migration of gastric cancer cells.

Conclusions

Here, we showed that the mRNA expression levels of ITGA2 comparing to normal tissues significantly increased. In addition, the results revealed that targeting integrin alpha 2 subunit by antibodies did not only inhibit cell migration, but also induce apoptosis effect on gastric cancer cells. Interestingly, higher expression level of ITGA2 led to significant effects on apoptosis progression during anti-ITGA2 antibody treatment, which indicated that ITGA2 expression levels directly correlate with their functionality. Our findings suggest that ITGA2 is a potential therapeutic target for gastric cancer.

Analysis of the Function of Apoptosis during Imaginal Wing Disc Regeneration in Drosophila melanogaster

Regeneration is the ability that allows organisms to replace missing organs or lost tissue after injuries. This ability requires the coordinated activity of different cellular processes, including programmed cell death. Apoptosis plays a key role as a source of signals necessary for regeneration in different organisms. The imaginal discs of Drosophila melanogaster provide a particularly well-characterised model system for studying the cellular and molecular mechanisms underlying regeneration. Although it has been shown that signals produced by apoptotic cells are needed for homeostasis and regeneration of some tissues of this organism, such as the adult midgut, the contribution of apoptosis to disc regeneration remains unclear. Using a new method for studying disc regeneration in physiological conditions, we have defined the pattern of cell death in regenerating discs. Our data indicate that during disc regeneration, cell death increases first at the wound edge, but as regeneration progresses dead cells can be observed in regions far away from the site of damage. This result indicates that apoptotic signals initiated in the wound spread throughout the disc. We also present results which suggest that the partial inhibition of apoptosis does not have a major effect on disc regeneration. Finally, our results suggest that during disc regeneration distinct apoptotic signals might be acting simultaneously.

The defender against apoptotic cell death 1 gene is required for tissue growth and efficient N-glycosylation in Drosophila melanogaster

How organ growth is regulated in multicellular organisms is a long-standing question in developmental biology. It is known that coordination of cell apoptosis and proliferation is critical in cell number and overall organ size control, while how these processes are regulated is still under investigation. In this study, we found that functional loss of a gene in Drosophila, named Drosophila defender against apoptotic cell death 1 (dDad1), leads to a reduction of tissue growth due to increased apoptosis and lack of cell proliferation. The dDad1 protein, an orthologue of mammalian Dad1, was found to be crucial for protein N-glycosylation in developing tissues. Our study demonstrated that loss of dDad1 function activates JNK signaling and blocking the JNK pathway in dDad1 knock-down tissues suppresses cell apoptosis and partially restores organ size. In addition, reduction of dDad1 triggers ER stress and activates unfolded protein response (UPR) signaling, prior to the activation of JNK signaling. Furthermore, Perk-Atf4 signaling, one branch of UPR pathways, appears to play a dual role in inducing cell apoptosis and mediating compensatory cell proliferation in this dDad1 knock-down model.

Disruption of the Cdc42/Par6/aPKC or Dlg/Scrib/Lgl Polarity Complex Promotes Epithelial Proliferation via Overlapping Mechanisms

The establishment and maintenance of apical-basal polarity is a defining characteristic and essential feature of functioning epithelia. Apical-basal polarity (ABP) proteins are also tumor suppressors that are targeted for disruption by oncogenic viruses and are commonly mutated in human carcinomas. Disruption of these ABP proteins is an early event in cancer development that results in increased proliferation and epithelial disorganization through means not fully characterized. Using the proliferating Drosophila melanogaster wing disc epithelium, we demonstrate that disruption of the junctional vs. basal polarity complexes results in increased epithelial proliferation via distinct downstream signaling pathways. Disruption of the basal polarity complex results in JNK-dependent proliferation, while disruption of the junctional complex primarily results in p38-dependent proliferation. Surprisingly, the Rho-Rok-Myosin contractility apparatus appears to play opposite roles in the regulation of the proliferative phenotype based on which polarity complex is disrupted. In contrast, non-autonomous Tumor Necrosis Factor (TNF) signaling appears to suppress the proliferation that results from apical-basal polarity disruption, regardless of which complex is disrupted. Finally we demonstrate that disruption of the junctional polarity complex activates JNK via the Rho-Rok-Myosin contractility apparatus independent of the cortical actin regulator, Moesin.

Jun N-terminal kinase signaling makes a face

decapentaplegic (dpp), the Drosophila ortholog of BMP 2/4, directs ventral adult head morphogenesis through expression in the peripodial epithelium of the eye-antennal disc. This dpp expressing domain exerts effects both on the peripodial epithelium, and the underlying disc proper epithelium. We have uncovered a role for the Jun N-terminal kinase (JNK) pathway in dpp-mediated ventral head development. JNK activity is required for dpp's action on the disc proper, but in the absence of dpp expression, excessive JNK activity is produced, leading to specific loss of maxillary palps. In this review we outline our hypotheses on how dpp acts by both short range and longer range mechanisms to direct head morphogenesis and speculate on the dual role of JNK signaling in this process. Finally, we describe the regulatory control of dpp expression in the eye-antennal disc, and pose the problem of how the various expression domains of a secreted protein can be targeted to their specific functions.

JNK/SAPK Signaling Is Essential for Efficient Reprogramming of Human Fibroblasts to Induced Pluripotent Stem Cells

Reprogramming of somatic cells to the phenotypic state termed “induced pluripotency” is thought to occur through three consecutive stages: initiation, maturation, and stabilisation. The initiation phase is stochastic but nevertheless very important as it sets the gene expression pattern that permits completion of reprogramming; hence a better understanding of this phase and how this is regulated may provide the molecular cues for improving the reprogramming process. c‐Jun N‐terminal kinase (JNK)/stress‐activated protein kinase (SAPKs) are stress activated MAPK kinases that play an essential role in several processes known to be important for successful completion of the initiation phase such as cellular proliferation, mesenchymal to epithelial transition (MET) and cell cycle regulation. In view of this, we postulated that manipulation of this pathway would have significant impacts on reprogramming of human fibroblasts to induced pluripotent stem cells. Accordingly, we found that key components of the JNK/SAPK signaling pathway increase expression as early as day 3 of the reprogramming process and continue to rise in reprogrammed cells throughout the initiation and maturation stages. Using both chemical inhibitors and RNA interference of MKK4, MKK7 and JNK1, we tested the role of JNK/SAPK signaling during the initiation stage of neonatal and adult fibroblast reprogramming. These resulted in complete abrogation of fully reprogrammed colonies and the emergence of partially reprogrammed colonies which disaggregated and were lost from culture during the maturation stage. Inhibition of JNK/SAPK signaling resulted in reduced cell proliferation, disruption of MET and loss of the pluripotent phenotype, which either singly or in combination prevented establishment of pluripotent colonies. Together these data provide new evidence for an indispensable role for JNK/SAPK signaling to overcome the well‐established molecular barriers in human somatic cell induced reprogramming. Stem Cells2016;34:1198–1212

The adaptor protein Cindr regulates JNK activity to maintain epithelial sheet integrity

Epithelia are essential barrier tissues that must be appropriately maintained for their correct function. To achieve this a plethora of protein interactions regulate epithelial cell number, structure and adhesion, and differentiation. Here we show that Cindr (the Drosophila Cin85 and Cd2ap ortholog) is required to maintain epithelial integrity. Reducing Cindr triggered cell delamination and movement. Most delaminating cells died. These behaviors were consistent with JNK activation previously associated with loss of epithelial integrity in response to ectopic oncogene activity. We confirmed a novel interaction between Cindr and Drosophila JNK (dJNK), which when perturbed caused inappropriate JNK signaling. Genetically reducing JNK signaling activity suppressed the effects of reducing Cindr. Furthermore, ectopic JNK signaling phenocopied loss of Cindr and was partially rescued by concomitant cindr over-expression. Thus, correct Cindr-dJNK stoichiometry is essential to maintain epithelial integrity and disturbing this balance may contribute to the pathogenesis of disease states, including cancer.

Dual Role of Jun N-Terminal Kinase Activity in Bone Morphogenetic Protein-Mediated Drosophila Ventral Head Development

The Drosophila bone morphogenetic protein encoded by decapentaplegic (dpp) controls ventral head morphogenesis by expression in the head primordia, eye-antennal imaginal discs. These are epithelial sacs made of two layers: columnar disc proper cells and squamous cells of the peripodial epithelium. dpp expression related to head formation occurs in the peripodial epithelium; cis-regulatory mutations disrupting this expression display defects in sensory vibrissae, rostral membrane, gena, and maxillary palps. Here we document that disruption of this dpp expression causes apoptosis in peripodial cells and underlying disc proper cells. We further show that peripodial Dpp acts directly on the disc proper, indicating that Dpp must cross the disc lumen to act. We demonstrate that palp defects are mechanistically separable from the other mutant phenotypes; both are affected by the c-Jun N-terminal kinase pathway but in opposite ways. Slight reduction of both Jun N-terminal kinase and Dpp activity in peripodial cells causes stronger vibrissae, rostral membrane, and gena defects than Dpp alone; additionally, strong reduction of Jun N-terminal kinase activity alone causes identical defects. A more severe reduction of dpp results in similar vibrissae, rostral membrane, and gena defects, but also causes mutant maxillary palps. This latter defect is correlated with increased peripodial Jun N-terminal kinase activity and can be caused solely by ectopic activation of Jun N-terminal kinase. We conclude that formation of sensory vibrissae, rostral membrane, and gena tissue in head morphogenesis requires the action of Jun N-terminal kinase in peripodial cells, while excessive Jun N-terminal kinase signaling in these same cells inhibits the formation of maxillary palps.

Crumbs is an essential regulator of cytoskeletal dynamics and cell-cell adhesion during dorsal closure in Drosophila

The evolutionarily conserved Crumbs protein is required for epithelial polarity and morphogenesis. Here we identify a novel role of Crumbs as a negative regulator of actomyosin dynamics during dorsal closure in the Drosophila embryo. Embryos carrying a mutation in the FERM (protein 4.1/ezrin/radixin/moesin) domain-binding motif of Crumbs die due to an overactive actomyosin network associated with disrupted adherens junctions. This phenotype is restricted to the amnioserosa and does not affect other embryonic epithelia. This function of Crumbs requires DMoesin, the Rho1-GTPase, class-I p21-activated kinases and the Arp2/3 complex. Data presented here point to a critical role of Crumbs in regulating actomyosin dynamics, cell junctions and morphogenesis.

DOI:http://dx.doi.org/10.7554/eLife.07398.001

A layer of epithelial cells covers the body surface of animals. Epithelial cells have a property known as polarity; this means that they have two different poles, one of which is in contact with the environment. Midway through embryonic development, the Drosophila embryo is covered by two kinds of epithelial sheets; the epidermis on the front, the belly and the sides of the embryo, and the amnioserosa on the back. In the second half of embryonic development, the amnioserosa is brought into the embryo in a process called dorsal closure, while the epidermis expands around the back of the embryo to encompass it.

One of the major activities driving dorsal closure is the contraction of amnioserosa cells. This contraction depends on the highly dynamic activity of the protein network that helps give cells their shape, known as the actomyosin cytoskeleton. One major question in the field is how changes in the actomyosin cytoskeleton are controlled as tissues take shape (a process known as “morphogenesis”) and how the integrity of epithelial tissues is maintained during these processes.

A key regulator of epidermal and amnioserosa polarity is an evolutionarily conserved protein called Crumbs. The epithelial tissues of mutant embryos that do not produce Crumbs lose polarity and integrity, and the embryos fail to develop properly.

Flores-Benitez and Knust have now studied the role of Crumbs in the morphogenesis of the amnioserosa during dorsal closure. This revealed that fly embryos that produce a mutant Crumbs protein that cannot interact with a protein called Moesin (which links the cell membrane and the actomyosin cytoskeleton) are unable to complete dorsal closure. Detailed analyses showed that this failure of dorsal closure is due to the over-activity of the actomyosin cytoskeleton in the amnioserosa. This results in increased and uncoordinated contractions of the cells, and is accompanied by defects in cell-cell adhesion that ultimately cause the amnioserosa to lose integrity. Flores-Benitez and Knust’s genetic analyses further showed that several different signalling systems participate in this process.

Flores-Benitez and Knust’s results reveal an unexpected role of Crumbs in coordinating polarity, actomyosin activity and cell-cell adhesion. Further work is now needed to understand the molecular mechanisms and interactions that enable Crumbs to coordinate these processes; in particular, to unravel how Crumbs influences the periodic contractions that drive changes in cell shape. It will also be important to investigate whether Crumbs is involved in similar mechanisms that operate in other developmental events in which actomyosin oscillations have been linked to tissue morphogenesis.

DOI:http://dx.doi.org/10.7554/eLife.07398.002

Fyn Activation of mTORC1 Stimulates the IRE1α-JNK Pathway, Leading to Cell Death

We previously reported that the skeletal muscle-specific overexpression of Fyn in mice resulted in a severe muscle wasting phenotype despite the activation of mTORC1 signaling. To investigate the bases for the loss of muscle fiber mass, we examined the relationship between Fyn activation of mTORC1, JNK, and endoplasmic reticulum stress. Overexpression of Fyn in skeletal muscle in vivo and in HEK293T cells in culture resulted in the activation of IRE1α and JNK, leading to increased cell death. Fyn synergized with the general endoplasmic reticulum stress inducer thapsigargin, resulting in the activation of IRE1α and further accelerated cell death. Moreover, inhibition of mTORC1 with rapamycin suppressed IRE1α activation and JNK phosphorylation, resulting in protecting cells against Fyn- and thapsigargin-induced cell death. Moreover, rapamycin treatment in vivo reduced the skeletal muscle IRE1α activation in the Fyn-overexpressing transgenic mice. Together, these data demonstrate the presence of a Fyn-induced endoplasmic reticulum stress that occurred, at least in part, through the activation of mTORC1, as well as subsequent activation of the IRE1α-JNK pathway driving cell death.

Rho1-Wnd signaling regulates loss-of-cell polarity-induced cell invasion in Drosophila

Both cell polarity and c-Jun N-terminal kinase (JNK) activity are essential to the maintenance of tissue homeostasis, and disruption of either is commonly seen in cancer progression. Despite the established connection between loss-of-cell polarity and JNK activation, much less is known about the molecular mechanism by which aberrant cell polarity induces JNK-mediated cell migration and tumor invasion. Here we show results from a genetic screen using an in vivo invasion model via knocking down cell polarity gene in Drosophila wing discs, and identify Rho1-Wnd signaling as an important molecular link that mediates loss-of-cell polarity-triggered JNK activation and cell invasion. We show that Wallenda (Wnd), a protein kinase of the mitogen-activated protein kinase kinase kinase family, by forming a complex with the GTPase Rho1, is both necessary and sufficient for Rho1-induced JNK-dependent cell invasion, MMP1 activation and epithelial-mesenchymal transition. Furthermore, Wnd promotes cell proliferation and tissue growth through wingless production when apoptosis is inhibited by p35. Finally, Wnd shows oncogenic cooperation with Ras(V12) to trigger tumor growth in eye discs and causes invasion into the ventral nerve cord. Together, our data not only provides a novel mechanistic insight on how cell polarity loss contributes to cell invasion, but also highlights the value of the Drosophila model system to explore human cancer biology.

Wallenda regulates JNK-mediated cell death in Drosophila

The c-Jun N-terminal kinase (JNK) pathway plays essential roles in regulating a variety of cellular processes including proliferation, migration and survival. Previous genetic studies in Drosophila have identified numerous cell death regulating genes, providing new insights into the mechanisms for related diseases. Despite the known role of the small GTPase Rac1 in regulating cell death, the downstream components and underlying mechanism remain largely elusive. Here, we show that Rac1 promotes JNK-dependent cell death through Wallenda (Wnd). In addition, we find that Wnd triggers JNK activation and cell death via its kinase domain. Moreover, we show that both MKK4 and Hep are critical for Wnd-induced cell death. Furthermore, Wnd is essential for ectopic Egr- or Rho1-induced JNK activation and cell death. Finally, Wnd is physiologically required for loss of scribble-induced JNK-dependent cell death. Thus, our data suggest that wnd encodes a novel essential cell death regulator in Drosophila.

The transmembrane protein Crumbs displays complex dynamics during follicular morphogenesis and is regulated competitively by Moesin and aPKC

The transmembrane protein Crumbs (Crb) functions in apical polarity and epithelial integrity. To better understand its role in epithelial morphogenesis, we examined Crb localization and dynamics in the late follicular epithelium of Drosophila. Crb was unexpectedly dynamic during middle-to-late stages of egg chamber development, being lost from the marginal zone (MZ) in stage 9 before abruptly returning at the end of stage 10b, then undergoing a pulse of endocytosis in stage 12. The reappearance of MZ Crb is necessary to maintain an intact adherens junction and MZ. Although Crb has been proposed to interact through its juxtamembrane domain with Moesin (Moe), a FERM domain protein that regulates the cortical actin cytoskeleton, the functional significance of this interaction is poorly understood. We found that whereas the Crb juxtamembrane domain was not required for adherens junction integrity, it was necessary for MZ localization of Moe, aPKC and F-actin. Furthermore, Moe and aPKC functioned antagonistically, suggesting that Moe limits Crb levels by reducing its interactions with the apical Par network. Additionally, Moe mutant cells lost Crb from the apical membrane and accumulated excess Crb at the MZ, suggesting that Moe regulates Crb distribution at the membrane. Together, these studies reveal reciprocal interactions between Crb, Moe and aPKC during cellular morphogenesis.

Impaired Hippo signaling promotes Rho1-JNK-dependent growth

The Hippo and c-Jun N-terminal kinase (JNK) pathway both regulate growth and contribute to tumorigenesis when dysregulated. Whereas the Hippo pathway acts via the transcription coactivator Yki/YAP to regulate target gene expression, JNK signaling, triggered by various modulators including Rho GTPases, activates the transcription factors Jun and Fos. Here, we show that impaired Hippo signaling induces JNK activation through Rho1. Blocking Rho1-JNK signaling suppresses Yki-induced overgrowth in the wing disk, whereas ectopic Rho1 expression promotes tissue growth when apoptosis is prohibited. Furthermore, Yki directly regulates Rho1 transcription via the transcription factor Sd. Thus, our results have identified a novel molecular link between the Hippo and JNK pathways and implicated the essential role of the JNK pathway in Hippo signaling-related tumorigenesis.

Viral vector-mediated downregulation of RhoA increases survival and axonal regeneration of retinal ganglion cells

The Rho/ROCK pathway is a promising therapeutic target in neurodegenerative and neurotraumatic diseases. Pharmacological inhibition of various pathway members has been shown to promote neuronal regeneration and survival. However, because pharmacological inhibitors are inherently limited in their specificity, shRNA-mediated approaches can add more information on the function of each single kinase involved. Thus, we generated adeno-associated viral vectors (AAV) to specifically downregulate Ras homologous member A (RhoA) via shRNA. We found that specific knockdown of RhoA promoted neurite outgrowth of retinal ganglion cells (RGC) grown on the inhibitory substrate chondroitin sulfate proteoglycan (CSPG) as well as neurite regeneration of primary midbrain neurons (PMN) after scratch lesion. In the rat optic nerve crush (ONC) model in vivo, downregulation of RhoA significantly enhanced axonal regeneration compared to control. Moreover, survival of RGC transduced with AAV expressing RhoA-shRNA was substantially increased at 2 weeks after optic nerve axotomy. Compared to previous data using pharmacological inhibitors to target RhoA, its upstream regulator Nogo or its main downstream target ROCK, the specific effects of RhoA downregulation shown here were most pronounced in regard to promoting RGC survival but neurite outgrowth and axonal regeneration were also increased significantly. Taken together, we show here that specific knockdown of RhoA substantially increases neuronal survival after optic nerve axotomy and modestly increases neurite outgrowth in vitro and axonal regeneration after optic nerve crush.

Venus kinase receptors control reproduction in the platyhelminth parasite Schistosoma mansoni

The Venus Kinase Receptor (VKR) is a single transmembrane molecule composed of an intracellular tyrosine kinase domain close to that of insulin receptor and an extracellular Venus Flytrap (VFT) structure similar to the ligand binding domain of many class C G Protein Coupled Receptors. This receptor tyrosine kinase (RTK) was first discovered in the platyhelminth parasite Schistosoma mansoni, then in a large variety of invertebrates. A single vkr gene is found in most genomes, except in S. mansoni in which two genes Smvkr1 and Smvkr2 exist. VKRs form a unique family of RTKs present only in invertebrates and their biological functions are still to be discovered. In this work, we show that SmVKRs are expressed in the reproductive organs of S. mansoni, particularly in the ovaries of female worms. By transcriptional analyses evidence was obtained that both SmVKRs fulfill different roles during oocyte maturation. Suppression of Smvkr expression by RNA interference induced spectacular morphological changes in female worms with a strong disorganization of the ovary, which was dominated by the presence of primary oocytes, and a defect of egg formation. Following expression in Xenopus oocytes, SmVKR1 and SmVKR2 receptors were shown to be activated by distinct ligands which are L-Arginine and calcium ions, respectively. Signalling analysis in Xenopus oocytes revealed the capacity of SmVKRs to activate the PI3K/Akt/p70S6K and Erk MAPK pathways involved in cellular growth and proliferation. Additionally, SmVKR1 induced phosphorylation of JNK (c-Jun N-terminal kinase). Activation of JNK by SmVKR1 was supported by the results of yeast two-hybrid experiments identifying several components of the JNK pathway as specific interacting partners of SmVKR1. In conclusion, these results demonstrate the functions of SmVKR in gametogenesis, and particularly in oogenesis and egg formation. By eliciting signalling pathways potentially involved in oocyte proliferation, growth and migration, these receptors control parasite reproduction and can therefore be considered as potential targets for anti-schistosome therapies.

Schistosomiasis is a chronic, debilitating disease affecting more than 200 million people in the world caused by parasitic flatworms of the genus Schistosoma. Pathology is mainly due to massive egg production by parasites and formation of granulomas around the eggs trapped in liver and different organs. Therefore, targeting the molecular processes responsible for gonad development or egg production in schistosomes appears as a valuable strategy to reduce pathogenesis and dissemination of schistosomiasis. In the present study, we investigated the importance of Venus Kinase Receptors (VKRs) which are unusual receptor tyrosine kinases (RTKs) with an extracellular Venus Flytrap (VFT) ligand-binding domain in the control of reproduction of schistosomes. SmVKRs are expressed in female ovaries of Schistosoma mansoni and the knock-down of their expression provoked dramatic alterations of the oocyte content in ovaries and reduction of egg formation. SmVKRs were also shown to activate different signalling pathways potentially involved in oocyte proliferation, growth and migration. Therefore our results demonstrate that VKRs are essential actors of oogenesis and egg formation in S. mansoni. Moreover, their presence in a large variety of invertebrate species including other helminth parasites and insect parasite vectors can open new perspectives in the control of various vector-borne infectious diseases.

Moesin functionality in hypothermic liver preservation injury

The objective of this study was to determine how expression and functionality of the cytoskeletal linker protein moesin is involved in hepatic hypothermic preservation injury. Mouse livers were cold stored in University of Wisconsin (UW) solution and reperfused on an isolated perfused liver (IPL) device for one hour. Human hepatocytes (HepG2) and human or murine sinusoidal endothelial cells (SECs) were cold stored and rewarmed to induce hypothermic preservation injury. The cells were transfected with: wild type moesin, an siRNA duplex specific for moesin, and the moesin mutants T558D and T558A. Tissue and cell moesin expression and its binding to actin were determined by Western blot. Liver IPL functional outcomes deteriorated proportional to the length of cold storage, which correlated with moesin disassociation from the actin cytoskeleton. Cell viability (LDH and WST-8) in the cell models progressively declined with increasing preservation time, which also correlated with moesin disassociation. Transfection of a moesin containing plasmid or an siRNA duplex specific for moesin into HepG2 cells resulted in increased and decreased moesin expression, respectively. Overexpression of moesin protected while moesin knock-down potentiated preservation injury in the HepG2 cell model. Hepatocytes expressing the T558A (inactive) and T558D (active) moesin binding mutants demonstrated significantly more and less preservation injury, respectively. Cold storage time dependently caused hepatocyte detachment from the matrix and cell death, which was prevented by the T558D active moesin mutation. In conclusion, moesin is causally involved in hypothermic liver cell preservation injury through control of its active binding molecular functionality.

Disruption of the protein kinase N gene of drosophila melanogaster results in the recessive delorean allele (pkndln) with a negative impact on wing morphogenesis

We describe the delorean mutation of the Drosophila melanogaster protein kinase N gene (pkn(dln)) with defects in wing morphology. Flies homozygous for the recessive pkn(dln) allele have a composite wing phenotype that exhibits changes in relative position and shape of the wing blade as well as loss of specific vein and bristle structures. The pkn(dln) allele is the result of a P-element insertion in the first intron of the pkn locus, and the delorean wing phenotype is contingent upon the interaction of insertion-bearing alleles in trans. The presence of the insertion results in production of a novel transcript that initiates from within the 3' end of the P-element. The delorean-specific transcript is predicted to produce a wild-type PKN protein. The delorean phenotype is not the result of a reduction in pkn expression, as it could not be recreated using a variety of wing-specific drivers of pkn-RNAi expression. Rather, it is the presence of the delorean-specific transcript that correlates with the mutant phenotype. We consider the delorean wing phenotype to be due to a pairing-dependent, recessive mutation that behaves as a dosage-sensitive, gain of function. Our analysis of genetic interactions with basket and nemo reflects an involvement of pkn and Jun-terminal kinase signaling in common processes during wing differentiation and places PKN as a potential effector of Rho1's involvement in the Jun-terminal kinase pathway. The delorean phenotype, with its associated defects in wing morphology, provides evidence of a role for PKN in adult morphogenetic processes.

STRIPAK complexes: structure, biological function, and involvement in human diseases

The mammalian striatin family consists of three proteins, striatin, S/G2 nuclear autoantigen, and zinedin. Striatin family members have no intrinsic catalytic activity, but rather function as scaffolding proteins. Remarkably, they organize multiple diverse, large signaling complexes that participate in a variety of cellular processes. Moreover, they appear to be regulatory/targeting subunits for the major eukaryotic serine/threonine protein phosphatase 2A. In addition, striatin family members associate with germinal center kinase III kinases as well as other novel components, earning these assemblies the name striatin-interacting phosphatase and kinase (STRIPAK) complexes. Recently, there has been a great increase in functional and mechanistic studies aimed at identifying and understanding the roles of STRIPAK and STRIPAK-like complexes in cellular processes of multiple organisms. These studies have identified novel STRIPAK and STRIPAK-like complexes and have explored their roles in specific signaling pathways. Together, the results of these studies have sparked increased interest in striatin family complexes because they have revealed roles in signaling, cell cycle control, apoptosis, vesicular trafficking, Golgi assembly, cell polarity, cell migration, neural and vascular development, and cardiac function. Moreover, STRIPAK complexes have been connected to clinical conditions, including cardiac disease, diabetes, autism, and cerebral cavernous malformation. In this review, we discuss the expression, localization, and protein domain structure of striatin family members. Then we consider the diverse complexes these proteins and their homologs form in various organisms, emphasizing what is known regarding function and regulation. Finally, we explore possible roles of striatin family complexes in disease, especially cerebral cavernous malformation.

Genetic models of apoptosis-induced proliferation decipher activation of JNK and identify a requirement of EGFR signaling for tissue regenerative responses in Drosophila

Recent work in several model organisms has revealed that apoptotic cells are able to stimulate neighboring surviving cells to undergo additional proliferation, a phenomenon termed apoptosis-induced proliferation. This process depends critically on apoptotic caspases such as Dronc, the Caspase-9 ortholog in Drosophila, and may have important implications for tumorigenesis. While it is known that Dronc can induce the activity of Jun N-terminal kinase (JNK) for apoptosis-induced proliferation, the mechanistic details of this activation are largely unknown. It is also controversial if JNK activity occurs in dying or in surviving cells. Signaling molecules of the Wnt and BMP families have been implicated in apoptosis-induced proliferation, but it is unclear if they are the only ones. To address these questions, we have developed an efficient assay for screening and identification of genes that regulate or mediate apoptosis-induced proliferation. We have identified a subset of genes acting upstream of JNK activity including Rho1. We also demonstrate that JNK activation occurs both in apoptotic cells as well as in neighboring surviving cells. In a genetic screen, we identified signaling by the EGFR pathway as important for apoptosis-induced proliferation acting downstream of JNK signaling. These data underscore the importance of genetic screening and promise an improved understanding of the mechanisms of apoptosis-induced proliferation.

Work in recent years has revealed that apoptotic caspases not only induce apoptosis, but also have non-apoptotic functions. One of these functions is apoptosis-induced proliferation, a relatively recently discovered phenomenon by which apoptotic cells induce proliferation of surviving neighboring cells. This phenomenon may have important implications for stem cell activity, tissue regeneration and tumorigenesis. Here, we describe the development of a genetic model of apoptosis-induced proliferation and the use of this model for convenient and unbiased genetic screening to identify genes involved in the process. We tested mutants of our RNAi transgenic lines targeting the core components of the apoptotic pathway and of JNK signaling, a known mediator of apoptosis-induced proliferation. These assays demonstrate the feasibility of the system for systematic genetic screening and identified several new genes upstream of JNK that are involved in apoptosis-induced proliferation. Finally, we tested the model in a pilot screen for chromosome arm 2L and identified spi, the EGF ligand in flies, as important for apoptosis-induced proliferation. We confirmed the involvement of EGF in a genuine apoptosis-induced regeneration system. These data underscore the importance of genetic screening and promise an improved understanding of the mechanisms of apoptosis-induced proliferation and regeneration.

Domain specificity of MAP3K family members, MLK and Tak1, for JNK signaling in Drosophila

A highly diverse set of protein kinases functions as early responders in the mitogen- and stress-activated protein kinase (MAPK/SAPK) signaling pathways. For instance, humans possess 14 MAPK kinase kinases (MAP3Ks) that activate Jun kinase (JNK) signaling downstream. A major challenge is to decipher the selective and redundant functions of these upstream MAP3Ks. Taking advantage of the relative simplicity of Drosophila melanogaster as a model system, we assessed MAP3K signaling specificity in several JNK-dependent processes during development and stress response. Our approach was to generate molecular chimeras between two MAP3K family members, the mixed lineage kinase, Slpr, and the TGF-β activated kinase, Tak1, which share 32% amino acid identity across the kinase domain but otherwise differ in sequence and domain structure, and then test the contributions of various domains for protein localization, complementation of mutants, and activation of signaling. We found that overexpression of the wild-type kinases stimulated JNK signaling in alternate contexts, so cells were capable of responding to both MAP3Ks, but with distinct outcomes. Relative to wild-type, the catalytic domain swaps compensated weakly or not at all, despite having a shared substrate, the JNK kinase Hep. Tak1 C-terminal domain-containing constructs were inhibitory in Tak1 signaling contexts, including tumor necrosis factor-dependent cell death and innate immune signaling; however, depressing antimicrobial gene expression did not necessarily cause phenotypic susceptibility to infection. These same constructs were neutral in the context of Slpr-dependent developmental signaling, reflecting differential subcellular protein localization and by inference, point of activation. Altogether, our findings suggest that the selective deployment of a particular MAP3K can be attributed in part to its inherent sequence differences, cellular localization, and binding partner availability.

Fluopsin C induces oncosis of human breast adenocarcinoma cells

AIM

Fluopsin C, an antibiotic isolated from Pseudomonas jinanesis, has shown antitumor effects on several cancer cell lines. In the current study, the oncotic cell death induced by fluopsin C was investigated in human breast adenocarcinoma cells in vitro.

METHODS

Human breast adenocarcinoma cell lines MCF-7 and MD-MBA-231 were used. The cytotoxicity was evaluated using MTT assay. Time-lapse microscopy and transmission electron microscopy were used to observe the morphological changes. Cell membrane integrity was assessed with propidium iodide (PI) uptake and lactate dehydrogenase (LDH) assay. Flow cytometry was used to measure reactive oxygen species (ROS) level and mitochondrial membrane potential (Δψm). A multimode microplate reader was used to analyze the intracellular ATP level. The changes in cytoskeletal system were investigated with Western blotting and immunostaining.

RESULTS

Fluopsin C (0.5-8 μmol/L) reduced the cell viability in dose- and time-dependent manners. Its IC50 values in MCF-7 and MD-MBA-231 cells at 24 h were 0.9 and 1.03 μmol/L, respectively. Fluopsin C (2 μmol/L) induced oncosis in both the breast adenocarcinoma cells characterized by membrane blebbing and swelling, which was blocked by pretreatment with the pan-caspase inhibitor Z-VAD-fmk. In MCF-7 cells, fluopsin C caused PI uptake into the cells, significantly increased LDH release, induced cytoskeletal system degradation and ROS accumulation, decreased the intracellular ATP level and Δψm. Noticeably, fluopsin C exerted comparable cytotoxicity against the normal human hepatocytes (HL7702) and human mammary epithelial cells with the IC50 values at 24 h of 2.7 and 2.4 μmol/L, respectively.

CONCLUSION

Oncotic cell death was involved in the anticancer effects of fluopsin C on human breast adenocarcinoma cells in vitro. The hepatoxicity of fluopsin C should not be ignored.

Cytotoxic triterpenoids from Lysimachia parvifolia

Five new oleanane-type triterpenoids, including two aglycones, 13β-28-epoxy-3β,22α,23-trihydroxyolean-16-one (1) and 13β-28-epoxy-22α,23-dihydroxyolean-3,16-dione (2), and three glycosides, anagalligenone-3-O-α-L-arabinopyranoside (3), anagalligenone-3-O-[β-D-glucopyranosyl(1 → 4)-α-L-arabinopyranoside] (4) and anagalligenone-3-O-[β-D-xylopyranosyl(1 → 2)-β-D-glucopyranosyl(1 → 4)-α-L-arabinopyranoside] (5), were isolated from the aerial parts of Lysimachia parvifolia, together with three known oleanane-type triterpenoid glycosides (6-8). The structures of the new compounds were subsequently elucidated by spectroscopic analysis and their cytotoxicities evaluated against six human cancer cell lines. Compounds 5-8 exhibited significant cytotoxicities against all the cell lines tested, with IC50 values lower than 10 μM. The possible mechanism of action of compound 6 was also studied.

Drosophila actin-Capping Protein limits JNK activation by the Src proto-oncogene

The Src family kinases c-Src, and its downstream effectors, the Rho family of small GTPases RhoA and Jun N-terminal kinase (JNK) have a significant role in tumorigenesis. In this report, using the Drosophila wing disc epithelium as a model system, we demonstrate that the actin-Capping Protein (CP) αβ heterodimer, which regulates actin filament (F-actin) polymerization, limits Src-induced apoptosis or tissue overgrowth by restricting JNK activation. We show that overexpressing Src64B drives JNK-independent loss of epithelial integrity and JNK-dependent apoptosis via Btk29A, p120ctn and Rho1. However, when cells are kept alive with the Caspase inhibitor P35, JNK acts as a potent inducer of proliferation via activation of the Yorkie oncogene. Reducing CP levels direct apoptosis of overgrowing Src64B-overexpressing tissues. Conversely, overexpressing capping protein inhibits Src64B and Rho1, but not Rac1-induced JNK signaling. CP requires the actin-binding domain of the α-subunit to limit Src64B-induced apoptosis, arguing that the control of F-actin mediates this effect. In turn, JNK directs F-actin accumulation. Moreover, overexpressing capping protein also prevents apoptosis induced by ectopic JNK expression. Our data are consistent with a model in which the control of F-actin by CP limits Src-induced apoptosis or tissue overgrowth by acting downstream of Btk29A, p120ctn and Rho1, but upstream of JNK. In turn, JNK may counteract the effect of CP on F-actin, providing a positive feedback, which amplifies JNK activation. We propose that cytoskeletal changes triggered by misregulation of F-actin modulators may have a significant role in Src-mediated malignant phenotypes during the early stages of cellular transformation.

Conundrum, an ARHGAP18 orthologue, regulates RhoA and proliferation through interactions with Moesin

RhoA, a small GTPase, regulates epithelial integrity and morphogenesis by controlling filamentous actin assembly and actomyosin contractility. Another important cytoskeletal regulator, Moesin (Moe), an ezrin, radixin, and moesin (ERM) protein, has the ability to bind to and organize cortical F-actin, as well as the ability to regulate RhoA activity. ERM proteins have previously been shown to interact with both RhoGEF (guanine nucleotide exchange factors) and RhoGAP (GTPase activating proteins), proteins that control the activation state of RhoA, but the functions of these interactions remain unclear. We demonstrate that Moe interacts with an unusual RhoGAP, Conundrum (Conu), and recruits it to the cell cortex to negatively regulate RhoA activity. In addition, we show that cortically localized Conu can promote cell proliferation and that this function requires RhoGAP activity. Surprisingly, Conu's ability to promote growth also appears dependent on increased Rac activity. Our results reveal a molecular mechanism by which ERM proteins control RhoA activity and suggest a novel linkage between the small GTPases RhoA and Rac in growth control.

Depletion of PtdIns(4,5)P₂ underlies retinal degeneration in Drosophila trp mutants

The prototypical transient receptor potential (TRP) channel is the major light-sensitive, and Ca(2+)-permeable channel in the microvillar photoreceptors of Drosophila. TRP channels are activated following hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P₂] by the key effector enzyme phospholipase C (PLC). Mutants lacking TRP channels undergo light-dependent retinal degeneration, as a consequence of the reduced Ca(2+) influx. It has been proposed that degeneration is caused by defects in the Ca(2+)-dependent visual pigment cycle, which result in accumulation of toxic phosphorylated metarhodopsin-arrestin complexes (MPP-Arr2). Here we show that two interventions, which prevent accumulation of MPP-Arr2, namely rearing under red light or eliminating the C-terminal rhodopsin phosphorylation sites, failed to rescue degeneration in trp mutants. Instead, degeneration in trp mutants reared under red light was rescued by mutation of PLC. Degeneration correlated closely with the light-induced depletion of PtdIns(4,5)P₂ that occurs in trp mutants due to failure of Ca(2+)-dependent inhibition of PLC. Severe retinal degeneration was also induced in the dark in otherwise wild-type flies by overexpression of a bacterial PtdInsPn phosphatase (SigD) to deplete PtdIns(4,5)P₂. In degenerating trp photoreceptors, phosphorylated Moesin, a PtdIns(4,5)P₂-regulated membrane-cytoskeleton linker essential for normal microvillar morphology, was found to delocalize from the rhabdomere and there was extensive microvillar actin depolymerisation. The results suggest that compromised light-induced Ca(2+) influx, due to loss of TRP channels, leads to PtdIns(4,5)P₂ depletion, resulting in dephosphorylation of Moesin, actin depolymerisation and disintegration of photoreceptor structure.

In Drosophila, RhoGEF2 cooperates with activated Ras in tumorigenesis through a pathway involving Rho1-Rok-Myosin-II and JNK signalling

The Ras oncogene contributes to ≈ 30% of human cancers, but alone is not sufficient for tumorigenesis. In a Drosophila screen for oncogenes that cooperate with an activated allele of Ras (Ras(ACT)) to promote tissue overgrowth and invasion, we identified the GTP exchange factor RhoGEF2, an activator of Rho-family signalling. Here, we show that RhoGEF2 also cooperates with an activated allele of a downstream effector of Ras, Raf (Raf(GOF)). We dissect the downstream pathways through which RhoGEF2 cooperates with Ras(ACT) (and Raf(GOF)), and show that RhoGEF2 requires Rho1, but not Rac, for tumorigenesis. Furthermore, of the Rho1 effectors, we show that RhoGEF2 + Ras (Raf)-mediated tumorigenesis requires the Rho kinase (Rok)-Myosin-II pathway, but not Diaphanous, Lim kinase or protein kinase N. The Rho1-Rok-Myosin-II pathway leads to the activation of Jun kinase (JNK), in cooperation with Ras(ACT). Moreover, we show that activation of Rok or Myosin II, using constitutively active transgenes, is sufficient for cooperative tumorigenesis with Ras(ACT), and together with Ras(ACT) leads to strong activation of JNK. Our results show that Rok-Myosin-II activity is necessary and sufficient for Ras-mediated tumorigenesis. Our observation that activation of Myosin II, which regulates Filamentous actin (F-actin) contractility without affecting F-actin levels, cooperates with Ras(ACT) to promote JNK activation and tumorigenesis, suggests that increased cell contractility is a key factor in tumorigenesis. Furthermore, we show that signalling via the Tumour necrosis factor (TNF; also known as Egr)-ligand-JNK pathway is most likely the predominant pathway that activates JNK upon Rok activation. Overall, our analysis highlights the need for further analysis of the Rok-Myosin-II pathway in cooperation with Ras in human cancers.

Parvin overexpression uncovers tissue-specific genetic pathways and disrupts F-actin to induce apoptosis in the developing epithelia in Drosophila

Parvin is a putative F-actin binding protein important for integrin-mediated cell adhesion. Here we used overexpression of Drosophila Parvin to uncover its functions in different tissues in vivo. Parvin overexpression caused major defects reminiscent of metastatic cancer cells in developing epithelia, including apoptosis, alterations in cell shape, basal extrusion and invasion. These defects were closely correlated with abnormalities in the organization of F-actin at the basal epithelial surface and of integrin-matrix adhesion sites. In wing epithelium, overexpressed Parvin triggered increased Rho1 protein levels, predominantly at the basal side, whereas in the developing eye it caused a rough eye phenotype and severely disrupted F-actin filaments at the retina floor of pigment cells. We identified genes that suppressed these Parvin-induced dominant effects, depending on the cell type. Co-expression of both ILK and the apoptosis inhibitor DIAP1 blocked Parvin-induced lethality and apoptosis and partially ameliorated cell delamination in epithelia, but did not rescue the elevated Rho1 levels, the abnormal organization of F-actin in the wing and the assembly of integrin-matrix adhesion sites. The rough eye phenotype was suppressed by coexpression of either PTEN or Wech, or by knock-down of Xrp1. Two main conclusions can be drawn from our studies: (1), high levels of cytoplasmic Parvin are toxic in epithelial cells; (2) Parvin in a dose dependent manner affects the organization of actin cytoskeleton in both wing and eye epithelia, independently of its role as a structural component of the ILK-PINCH-Parvin complex that mediates the integrin-actin link. Thus, distinct genetic interactions of Parvin occur in different cell types and second site modifier screens are required to uncover such genetic circuits.

The apical polarity protein network in Drosophila epithelial cells: regulation of polarity, junctions, morphogenesis, cell growth, and survival

Epithelial tissue formation and function requires the apical-basal polarization of individual epithelial cells. Apical polarity regulators (APRs) are an evolutionarily conserved group of key factors that govern polarity and several other aspects of epithelial differentiation. APRs compose a diverse set of molecules including a transmembrane protein (Crumbs), a serine/threonine kinase (aPKC), a lipid phosphatase (PTEN), a small GTPase (Cdc42), FERM domain proteins (Moesin, Yurt), and several adaptor or scaffolding proteins (Bazooka/Par3, Par6, Stardust, Patj). These proteins form a dynamic cooperative network that is engaged in negative-feedback regulation with basolateral polarity factors to set up the epithelial apical-basal axis. APRs support the formation of the apical junctional complex and the segregation of the junctional domain from the apical membrane. It is becoming increasingly clear that APRs interact with the cytoskeleton and vesicle trafficking machinery, regulate morphogenesis, and modulate epithelial cell growth and survival. Not surprisingly, APRs have multiple fundamental links to human diseases such as cancer and blindness.

Drosophila heat shock response requires the JNK pathway and phosphorylation of mixed lineage kinase at a conserved serine-proline motif

Defining context specific requirements for proteins and pathways is a major challenge in the study of signal transduction. For example, the stress-activated protein kinase (SAPK) pathways are comprised of families of closely related transducers that are activated in a variety of tissues and contexts during development and organismal homeostasis. Consequently, redundant and pleiotropic effects have hampered a complete understanding of the individual contributions of transducers in distinct contexts. Here, we report on the function of a context-specific regulatory phosphorylation site, PXSP, in the Drosophila mixed lineage kinase protein, Slpr, a mitogen-activated protein kinase kinase kinase (MAP3K) in the Jun Kinase (JNK) pathway. Genetic analysis of the function of non-phosphorylatable (PXAP) and phosphomimetic mutant (PXEP) Slpr transgenes in several distinct contexts revealed minimal effects in JNK-dependent tissue closure processes but differential requirements in heat stress response. In particular, PXAP expression resulted in sensitivity of adults to sustained heat shock, like p38 and JNK pathway mutants. In contrast, PXEP overexpression conferred some resistance. Indeed, phosphorylation of the PXSP motif is enriched under heat shock conditions and requires in part, the p38 kinases for the enrichment. These data suggest that coordination of signaling between p38 and Slpr serves to maintain JNK signaling during heat stress. In sum, we demonstrate a novel role for JNK signaling in the heat shock response in flies and identify a posttranslational modification on Slpr, at a conserved site among MAP3K mixed lineage kinase family members, which bolsters stress resistance with negligible effects on JNK-dependent developmental processes.