Pro-apoptotic and pro-proliferation functions of the JNK pathway of Drosophila: roles in cell competition, tumorigenesis and regeneration

Regeneration following tissue necrosis is mediated by non-apoptotic caspase activity

Tissue necrosis is a devastating complication for many human diseases and injuries. Unfortunately, our understanding of necrosis and how it impacts surrounding healthy tissue - an essential consideration when developing effective methods to treat such injuries - has been limited by a lack of robust genetically tractable models. Our lab previously established a method to study necrosis-induced regeneration in the Drosophila wing imaginal disc, which revealed a unique phenomenon whereby cells at a distance from the injury upregulate caspase activity in a process called Necrosis-induced Apoptosis (NiA) that is vital for regeneration. Here we have further investigated this phenomenon, showing that NiA is predominantly associated with the highly regenerative pouch region of the disc, shaped by genetic factors present in the presumptive hinge. Furthermore, we find that a proportion of NiA fail to undergo apoptosis, instead surviving effector caspase activation to persist within the tissue and stimulate reparative proliferation late in regeneration. This proliferation relies on the initiator caspase Dronc, and occurs independent of JNK, ROS or mitogens associated with the previously characterized Apoptosis-induced Proliferation (AiP) mechanism. These data reveal a new means by which non-apoptotic Dronc signaling promotes regenerative proliferation in response to necrotic damage.

The JNK signaling pathway in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) serves as the underlying pathology for various spinal degenerative conditions and is a primary contributor to low back pain (LBP). Recent studies have revealed a strong correlation between IDD and biological processes such as Programmed Cell Death (PCD), cellular senescence, inflammation, cell proliferation, extracellular matrix (ECM) degradation, and oxidative stress (OS). Of particular interest is the emerging evidence highlighting the significant involvement of the JNK signaling pathway in these fundamental biological processes of IDD. This paper explores the potential mechanisms through the JNK signaling pathway influences IDD in diverse ways. The objective of this article is to offer a fresh perspective and methodology for in-depth investigation into the pathogenesis of IDD by thoroughly examining the interplay between the JNK signaling pathway and IDD. Moreover, this paper summarizes the drugs and natural compounds that alleviate the progression of IDD by regulating the JNK signaling pathway. This paper aims to identify potential therapeutic targets and strategies for IDD treatment, providing valuable insights for clinical application.

Exposure to the herbicide tebuthiuron affects behavior, enzymatic activity, morphology and physiology of the midgut of the stingless bee Partamona helleri

Partamona helleri is an important pollinator in the Neotropics. However, this bee faces an increased risk of pesticide exposure, potentially affecting both individual bees and entire colonies. Thus, this study aimed to evaluate the effects of the herbicide tebuthiuron on behavior, antioxidant activity, midgut morphology, and signaling pathways related to cell death, cell proliferation and differentiation in P. helleri workers. tebuthiuron significantly reduced locomotor activity and induced morphological changes in the midgut. The activity of the detoxification enzymes superoxide dismutase and glutathione S-transferase increased after exposure, indicating a detoxification mechanism. Furthermore, the herbicide led to alterations in the number of positive cells for signaling-pathway proteins in the midgut of bees, suggesting induction of apoptotic cell death and disruption of midgut epithelial regeneration. Therefore, tebuthiuron may negatively impact the behavior, antioxidant activity, morphology, and physiology of P. helleri workers, potentially posing a threat to the survival of this non-target organism.

Inter-cell type interactions that control JNK signaling in the Drosophila intestine

JNK signaling is a critical regulator of inflammation and regeneration, but how it is controlled in specific tissue contexts remains unclear. Here we show that, in the Drosophila intestine, the TNF-type ligand, Eiger (Egr), is expressed exclusively by intestinal stem cells (ISCs) and enteroblasts (EBs), where it is induced by stress and during aging. Egr preferentially activates JNK signaling in a paracrine fashion in differentiated enterocytes (ECs) via its receptor, Grindelwald (Grnd). N-glycosylation genes (Alg3, Alg9) restrain this activation, and stress-induced downregulation of Alg3 and Alg9 correlates with JNK activation, suggesting a regulatory switch. JNK activity in ECs induces expression of the intermembrane protease Rhomboid (Rho), driving secretion of EGFR ligands Keren (Krn) and Spitz (Spi), which in turn activate EGFR signaling in progenitor cells (ISCs and EBs) to stimulate their growth and division, as well as to produce more Egr. This study uncovers an N-glycosylation-controlled, paracrine JNK-EGFR-JNK feedforward loop that sustains ISC proliferation during stress-induced gut regeneration.

Exposure to low-concentration fipronil impairs survival, behavior, midgut morphology and physiology of Aedes aegypti larvae

The Aedes aegypti mosquito is a vector for various arboviruses, including dengue and yellow fever. Insecticides, such as pyrethroids and organophosphates, are widely used to manage and control these insects. However, mosquitoes have developed resistance to these chemicals. Therefore, this study aimed to investigate the effects of the commercial formulation of fipronil (Tuit® Florestal; 80% purity) on the survival, behavior, morphology, and proteins related to signaling pathways of the midgut in A. aegypti larvae under controlled laboratory conditions. Significant reductions in immature survival were observed in all concentrations of fipronil tested. Low insecticide concentration (0.5 ppb) led to decreased locomotor activity in the larvae and caused disorganization of the epithelial tissue in the midgut. Moreover, exposure to the insecticide decreased the activity of detoxifying enzymes such as catalase, superoxide dismutase, and glutathione-S-transferase. On the other hand, the insecticide increased protein oxidation and nitric oxide levels. The detection of LC3, caspase-3, and JNK proteins, related to autophagy and apoptosis, increased after exposure. However, there was a decrease in the positive cells for ERK 1/2. Furthermore, the treatment with fipronil decreased the number of positive cells for the proteins FMRF, Prospero, PH3, Wg, Armadillo, Notch, and Delta, which are related to cell proliferation and differentiation. These findings demonstrate that even at low concentrations, fipronil exerts larvicidal effects on A. aegypti by affecting behavior and enzymatic detoxification, inducing protein oxidation, free radical generation, midgut damage and cell death, and inhibiting cell proliferation and differentiation. Thus, this insecticide may represent a viable alternative for controlling the spread of this vector.

Regulation of Notch signaling by non-muscle myosin II Zipper in Drosophila

The Notch pathway is an evolutionarily conserved signaling system that is intricately regulated at multiple levels and it influences different aspects of development. In an effort to identify novel components involved in Notch signaling and its regulation, we carried out protein interaction screens which identified non-muscle myosin II Zipper (Zip) as an interacting partner of Notch. Physical interaction between Notch and Zip was further validated by co-immunoprecipitation studies. Immunocytochemical analyses revealed that Notch and Zip co-localize within same cytoplasmic compartment. Different alleles of zip also showed strong genetic interactions with Notch pathway components. Downregulation of Zip resulted in wing phenotypes that were reminiscent of Notch loss-of-function phenotypes and a perturbed expression of Notch downstream targets, Cut and Deadpan. Further, synergistic interaction between Notch and Zip resulted in highly ectopic expression of these Notch targets. Activated Notch-induced tumorous phenotype of larval tissues was enhanced by over-expression of Zip. Notch-Zip synergy resulted in the activation of JNK pathway that consequently lead to MMP activation and proliferation. Taken together, our results suggest that Zip may play an important role in regulation of Notch signaling.

RF, Mohan H, Annaert W, Chaudhary V. Maintenance of proteostasis by Drosophila Rer1 is essential for competitive cell survival and Myc-driven overgrowth

Defects in protein homeostasis can induce proteotoxic stress, affecting cellular fitness and, consequently, overall tissue health. In various growing tissues, cell competition based mechanisms facilitate detection and elimination of these compromised, often referred to as 'loser', cells by the healthier neighbors. The precise connection between proteotoxic stress and competitive cell survival remains largely elusive. Here, we reveal the function of an endoplasmic reticulum (ER) and Golgi localized protein Rer1 in the regulation of protein homeostasis in the developing Drosophila wing epithelium. Our results show that loss of Rer1 leads to proteotoxic stress and PERK-mediated phosphorylation of eukaryotic initiation factor 2α. Clonal analysis showed that rer1 mutant cells are identified as losers and eliminated through cell competition. Interestingly, we find that Rer1 levels are upregulated upon Myc-overexpression that causes overgrowth, albeit under high proteotoxic stress. Our results suggest that increased levels of Rer1 provide cytoprotection to Myc-overexpressing cells by alleviating the proteotoxic stress and thereby supporting Myc-driven overgrowth. In summary, these observations demonstrate that Rer1 acts as a novel regulator of proteostasis in Drosophila and reveal its role in competitive cell survival.

The Lifespan of D. melanogaster Depends on the Function of the Gagr Gene, a Domesticated gag Gene of Drosophila LTR Retrotransposons

(1) Background: The Gagr gene in Drosophila melanogaster's genome originated from the molecular domestication of retrotransposons and retroviruses' gag gene. In all Drosophila species, the Gagr protein homologs exhibit a conserved structure, indicative of a vital role. Previous studies have suggested a potential link between the Gagr gene function and stress responses. (2) Methods: We compared flies with Gagr gene knockdown in all tissues to control flies in physiological tests and RNA-sequencing experiments. (3) Results: Flies with the Gagr gene knockdown exhibited shorter lifespans compared to control flies. Transcriptome analysis revealed that Gagr knockdown flies showed elevated transcription levels of immune response genes. We used ammonium persulfate, a potent stress inducer, to elicit a stress response. In control flies, ammonium persulfate activated the Toll, JAK/STAT, and JNK/MAPK signaling pathways. In contrast, flies with the Gagr gene knockdown displayed reduced expression of stress response genes. Gene ontology enrichment analysis identified categories of genes upregulated under ammonium persulfate stress in control flies but not in Gagr knockdown flies. These genes are involved in developmental control, morphogenesis, and central nervous system function. (4) Conclusion: Our findings indicate the significance of the Gagr gene in maintaining immune response and homeostasis.

Exposure to sublethal concentrations of imidacloprid, pyraclostrobin, and glyphosate harm the behavior and fat body cells of the stingless bee Scaptotrigona postica

Pesticide use in agriculture threatens non-target insects such as bees. Considering the ecological and economic relevance of native bees, such as Scaptotrigona postica, and the insufficient studies on the effects of pesticides on their behavior and physiology, improving the current knowledge on this issue is essential. Therefore, this study investigated the sublethal effects of imidacloprid, pyraclostrobin, and glyphosate on the behavior and fat body cells of S. postica. Pesticide ingestion decreased the walking distance and mean velocity of bees compared to the control and solvent control groups. The oenocytes of the control groups were spherical, with central nuclei containing decondensed chromatin, and the trophocytes presented irregular morphology, with cells varying in shape and the cytoplasm filled with vacuoles and granules. However, bees exposed to pesticides showed extensive cytoarchitectural disruption in the fat body, such as vacuolization and shape changes in oenocytes and altered nuclei morphology in trophocytes. Moreover, pesticide exposure increased the number of atypical oenocytes and altered trophocytes, except for the PYR group, which showed a lower number of atypical oenocytes. Caspase-positive labeling significantly increased in all exposed bee groups. Alternatively, TLR4 labeling was significantly decreased in the exposed groups compared to the control groups. There was a significant increase in HSP90 immunolabeling in all exposed groups compared to the control. These findings reinforce the importance of research on the sublethal effects of low pesticide concentrations on key neotropical pollinators and prove that these toxic substances can impair their detoxification and immune defense.

Excess dietary sugar impairs Drosophila adult stem cells via elevated reactive oxygen species-induced JNK signaling

High-sugar diets (HSDs) often lead to obesity and type 2 diabetes, both metabolic syndromes associated with stem cell dysfunction. However, it is unclear whether excess dietary sugar affects stem cells. Here, we report that HSD impairs stem cell function in the intestine and ovaries of female Drosophila prior to the onset of insulin resistance, a hallmark of type 2 diabetes. Although 1 week of HSD leads to obesity, impaired oogenesis and altered lipid metabolism, insulin resistance does not occur. HSD increases glucose uptake by germline stem cells (GSCs) and triggers reactive oxygen species-induced JNK signaling, which reduces GSC proliferation. Removal of excess sugar from the diet reverses these HSD-induced phenomena. A similar phenomenon is found in intestinal stem cells (ISCs), except that HSD disrupts ISC maintenance and differentiation. Interestingly, tumor-like GSCs and ISCs are less responsive to HSD, which may be because of their dependence on glycolytic metabolism and high energy demand, respectively. This study suggests that excess dietary sugar induces oxidative stress and damages stem cells before insulin resistance develops, a mechanism that may also occur in higher organisms.

Nacα protects the larval fat body from cell death by maintaining cellular proteostasis in Drosophila

Protein homeostasis (proteostasis) is crucial for the maintenance of cellular homeostasis. Impairment of proteostasis activates proteotoxic and unfolded protein response pathways to resolve cellular stress or induce apoptosis in damaged cells. However, the responses of individual tissues to proteotoxic stress and evoking cell death program have not been extensively explored in vivo. Here, we show that a reduction in Nascent polypeptide-associated complex protein alpha subunit (Nacα) specifically and progressively induces cell death in Drosophila fat body cells. Nacα mutants disrupt both ER integrity and the proteasomal degradation system, resulting in caspase activation through JNK and p53. Although forced activation of the JNK and p53 pathways was insufficient to induce cell death in the fat body, the reduction of Nacα sensitized fat body cells to intrinsic and environmental stresses. Reducing overall protein synthesis by mTor inhibition or Minute mutants alleviated the cell death phenotype in Nacα mutant fat body cells. Our work revealed that Nacα is crucial for protecting the fat body from cell death by maintaining cellular proteostasis, thus demonstrating the coexistence of a unique vulnerability and cell death resistance in the fat body.

Lack of apoptosis leads to cellular senescence and tumorigenesis in Drosophila epithelial cells

Programmed cell death (apoptosis) is a homeostasis program of animal tissues designed to remove cells that are unwanted or are damaged by physiological insults. To assess the functional role of apoptosis, we have studied the consequences of subjecting Drosophila epithelial cells defective in apoptosis to stress or genetic perturbations that normally cause massive cell death. We find that many of those cells acquire persistent activity of the JNK pathway, which drives them into senescent status, characterized by arrest of cell division, cell hypertrophy, Senescent Associated ß-gal activity (SA-ß-gal), reactive oxygen species (ROS) production, Senescent Associated Secretory Phenotype (SASP) and migratory behaviour. We have identified two classes of senescent cells in the wing disc: 1) those that localize to the appendage part of the disc, express the upd, wg and dpp signalling genes and generate tumour overgrowths, and 2) those located in the thoracic region do not express wg and dpp nor they induce tumour overgrowths. Whether to become tumorigenic or non-tumorigenic depends on the original identity of the cell prior to the transformation. We also find that the p53 gene contributes to senescence by enhancing the activity of JNK.

Spoonbill positively regulates JNK signalling mediated apoptosis in Drosophila melanogaster

A-kinase anchoring protein (AKAP) comprises a family of scaffold proteins, which decides the subcellular localisation of a combination of signalling molecules. Spoonbill (Spoon) is a putative A-kinase anchoring protein in Drosophila. We have earlier reported that Spoon suppresses ribonuclear foci formed by trinucleotide repeat expanded transcripts associated with Spinocerebellar Ataxia 8 neurodegeneration in Drosophila. However, the role of Spoonbill in cellular signalling was unexplored. In this report, we have unravelled a novel function of Spoon protein in the regulation of the apoptotic pathway. The Drosophila TNFα homolog, Eiger, induces apoptosis via activation of the JNK pathway. We have shown here that Spoonbill is a positive regulator of the Eiger-induced JNK signalling. Further genetic interaction studies show that the spoon interacts with components of the JNK pathway, TGF-β activated kinase 1 (Tak1 - JNKKK), hemipterous (hep - JNKK) and basket (bsk - JNK). Interestingly, Spoonbill alone can also induce ectopic activation of the JNK pathway in a context-specific manner. To understand the molecular mechanism underlying Spoonbill-mediated modulation of the JNK pathway, the interaction between Spoon and Drosophila JNK was assessed. basket encodes the only known JNK in Drosophila. This serine/threonine-protein kinase phosphorylates Jra/Kay, which transcriptionally regulate downstream targets like Matrix metalloproteinase 1 (Mmp1), puckered (puc), and proapoptotic genes hid, reaper and grim. Interestingly, we found that Spoonbill colocalises and co-immunoprecipitates with the Basket protein in the developing photoreceptor neurons. Hence, we propose that Spoon plays a vital role in JNK-induced apoptosis. Furthermore, stress-induced JNK activation underlying Parkinson's Disease was also examined. In the Parkinson's Drosophila model of neurodegeneration, depletion of Spoonbill leads to a partial reduction of JNK pathway activation, along with improvement in adult motor activity. These observations suggest that the putative scaffold protein Spoonbill is a functional and physical interacting partner of the Drosophila JNK protein, Basket. Spoon protein is localised on the outer mitochondrial membrane (OMM), which may perhaps provide a suitable subcellular niche for activation of Drosophila Basket protein by its kinases which induce apoptosis.

Gbb Regulates Blood Cell Proliferation and Differentiation through JNK and EGFR Signaling Pathways in the Drosophila Lymph Gland

The Drosophila lymph gland is an ideal model for studying hematopoiesis, and unraveling the mechanisms of Drosophila hematopoiesis can improve our understanding of the pathogenesis of human hematopoietic malignancies. Bone morphogenetic protein (BMP) signaling is involved in a variety of biological processes and is highly conserved between Drosophila and mammals. Decapentaplegic (Dpp)/BMP signaling is known to limit posterior signaling center (PSC) cell proliferation by repressing the protooncogene dmyc. However, the role of two other TGF-β family ligands, Glass bottom boat (Gbb) and Screw (Scw), in Drosophila hematopoiesis is currently largely unknown. Here, we showed that the loss of Gbb in the cortical zone (CZ) induced lamellocyte differentiation by overactivation of the EGFR and JNK pathways and caused excessive differentiation of plasmatocytes, mainly by the hyperactivation of EGFR. Furthermore, we found that Gbb was also required for preventing the hyperproliferation of the lymph glands by inhibiting the overactivation of the Epidermal Growth Factor Receptor (EGFR) and c-Jun N-terminal Kinase (JNK) pathways. These results further advance our understanding of the roles of Gbb protein and the BMP signaling in Drosophila hematopoiesis and the regulatory relationship between the BMP, EGFR, and JNK pathways in the proliferation and differentiation of lymph gland hemocytes.

Bilateral JNK activation is a hallmark of interface surveillance and promotes elimination of aberrant cells

Tissue-intrinsic defense mechanisms eliminate aberrant cells from epithelia and thereby maintain the health of developing tissues or adult organisms. 'Interface surveillance' comprises one such distinct mechanism that specifically guards against aberrant cells which undergo inappropriate cell fate and differentiation programs. The cellular mechanisms which facilitate detection and elimination of these aberrant cells are currently unknown. We find that in Drosophila imaginal discs, clones of cells with inappropriate activation of cell fate programs induce bilateral JNK activation at clonal interfaces, where wild type and aberrant cells make contact. JNK activation is required to drive apoptotic elimination of interface cells. Importantly, JNK activity and apoptosis are highest in interface cells within small aberrant clones, which likely supports the successful elimination of aberrant cells when they arise. Our findings are consistent with a model where clone size affects the topology of interface contacts and thereby the strength of JNK activation in wild type and aberrant interface cells. Bilateral JNK activation is unique to 'interface surveillance' and is not observed in other tissue-intrinsic defense mechanisms, such as classical 'cell-cell competition'. Thus, bilateral JNK interface signaling provides an independent tissue-level mechanism to eliminate cells with inappropriate developmental fate but normal cellular fitness. Finally, oncogenic Ras-expressing clones activate 'interface surveillance' but evade elimination by bilateral JNK activation. Combined, our work establishes bilateral JNK interface signaling and interface apoptosis as a new hallmark of interface surveillance and highlights how oncogenic mutations evade tumor suppressor function encoded by this tissue-intrinsic surveillance system.

Xenobiotic responses of Drosophila melanogaster to insecticides with different modes of action and entry

Depending on their chemical structure, insecticides enter the insect body either through the cuticle or by ingestion (mode of entry [MoE]), and, naturally, harm or even kill insects through different mechanisms (modes of action). In parallel, they trigger a systemic detoxification response, especially by activation of detoxification gene expression. We monitored the acute genetic alterations of known xenobiotic response target genes against five different insecticides with two most common MoEs (contact toxicity and stomach toxicity), found that: 1. only a few genes were detected responding to acute exposure to insecticides (LD₉₀ ); 2. The expression of cyp12d1 was upregulated in all experiments, except for dichlorodiphenyltrichloroethane exposure, suggesting that cyp12d1 is a general first response gene of the xenobiotic response; 3. The contact and stomach entries did not show any notable difference, both MoEs induced the response of JNK signaling pathway, possibly serving as the driver of the response of cyp12d1 and a few other genes. In conclusion, the changes in gene expression levels were relatively modest and no significant differences were found between the two MoEs, so the insecticide entry route does not seem to have an impact on the detoxification response. However, the two MoEs of the same insecticide showed different efficiencies in our test. Thus, the study of these two MoEs will help to develop more efficient release and management methods for the use of such insecticides.

Fipronil exposure compromises respiration and damages the Malpighian tubules of the stingless bee Partamona helleri Friese (Hymenoptera: Apidae)

Fipronil has been widely used in agriculture and forestry in Brazil to control several pests. However, this insecticide may be hazardous to non-target organisms, including stingless bees, which are essential pollinators of crops and natural environments. Here, we investigated the effect of 24-h acute oral exposure to LC₅₀ of fipronil on the Malpighian tubules of the stingless bee Partamona helleri (Friese). Insecticide exposure decreases the respiration rate of forager bees, and the Malpighian tubules are severely affected, as shown by the epithelial architecture disorganization, loss of cytoplasmic content, degradation of the brush border, and nuclear pyknosis. In addition, fipronil ingestion increases the number of Malpighian cells positive for peroxidase, LC3, cleaved caspase-3, and JNK. However, Notch and ERK1/2-positive cells decrease in the exposed bees. These changes in the signaling proteins indicate an increase in oxidative stress, autophagy and apoptosis, and impairment of cell recovery. Overall, our results demonstrate the toxicological effects of fipronil on a stingless bee, which compromises the physiology of this important pollinator.

Imaginal Disc Regeneration: Something Old, Something New

Imaginal discs are simple epithelial sacs found in Drosophila larvae, which generate adult structures including wings and legs. The first studies of imaginal disc regeneration involved technically challenging transplantation experiments. Yet despite the difficulty, many aspects of regeneration including wound healing, blastema formation, and the repatterning of regenerated tissue were characterized. An important discovery was the phenomenon of transdetermination, where a small group of cells in regenerating tissue collectively switch fate ("collective cell reprogramming"). The development of genetic tissue-ablation systems over the last 12 years has energized this field, by making experiments less technically challenging, more reproducible, and by incorporating additional genetic analysis. Recent progress includes defining mechanistic links between early responses to wounding and the signaling pathways that drive proliferation, uncovering a role for localized silencing of damage-responsive enhancers to limit regenerative capacity as tissues mature, and identifying genes that maintain cellular plasticity within acceptable limits during regeneration.

The sooner, the better: ROS, kinases and nutrients at the onset of the damage response in Drosophila

One of the main topics in regeneration biology is the nature of the early signals that trigger the damage response. Recent advances in Drosophila point to the MAP3 kinase Ask1 as a molecular hub that integrates several signals at the onset of regeneration. It has been discovered that reactive oxygen species (ROS) produced in damaged imaginal discs and gut epithelia will activate the MAP3 kinase Ask1. Severely damaged and apoptotic cells produce an enormous amount of ROS, which ensures their elimination by activating Ask1 and in turn the pro-apoptotic function of JNK. However, this creates an oxidative stress environment with beneficial effects that is sensed by neighboring healthy cells. This environment, in addition to the Pi3K/Akt nutrient sensing pathway, can be integrated into Ask1 to launch regeneration. Ultimately the activity of Ask1 depends on these and other inputs and modulates its signaling to achieve moderate levels of p38 and low JNK signaling and thus promote survival and regeneration. This model based on the dual function of Ask1 for early response to damage is discussed here.

The Role of PKC-MAPK Signalling Pathways in the Development of Hyperglycemia-Induced Cardiovascular Complications

Cardiovascular disease is the most common cause of death among diabetic patients worldwide. Hence, cardiovascular wellbeing in diabetic patients requires utmost importance in disease management. Recent studies have demonstrated that protein kinase C activation plays a vital role in the development of cardiovascular complications via its activation of mitogen-activated protein kinase (MAPK) cascades, also known as PKC-MAPK pathways. In fact, persistent hyperglycaemia in diabetic conditions contribute to preserved PKC activation mediated by excessive production of diacylglycerol (DAG) and oxidative stress. PKC-MAPK pathways are involved in several cellular responses, including enhancing oxidative stress and activating signalling pathways that lead to uncontrolled cardiac and vascular remodelling and their subsequent dysfunction. In this review, we discuss the recent discovery on the role of PKC-MAPK pathways, the mechanisms involved in the development and progression of diabetic cardiovascular complications, and their potential as therapeutic targets for cardiovascular management in diabetic patients.

Non-apoptotic activation of Drosophila caspase-2/9 modulates JNK signaling, the tumor microenvironment, and growth of wound-like tumors

Resistance to apoptosis due to caspase deregulation is considered one of the main hallmarks of cancer. However, the discovery of novel non-apoptotic caspase functions has revealed unknown intricacies about the interplay between these enzymes and tumor progression. To investigate this biological problem, we capitalized on a Drosophila tumor model with human relevance based on the simultaneous overactivation of the EGFR and the JAK/STAT signaling pathways. Our data indicate that widespread non-apoptotic activation of initiator caspases limits JNK signaling and facilitates cell fate commitment in these tumors, thus preventing the overgrowth and exacerbation of malignant features of transformed cells. Intriguingly, caspase activity also reduces the presence of macrophage-like cells with tumor-promoting properties in the tumor microenvironment. These findings assign tumor-suppressing activities to caspases independent of apoptosis, while providing molecular details to better understand the contribution of these enzymes to tumor progression.

Cell autonomous and non-autonomous consequences of deviations in translation machinery on organism growth and the connecting signalling pathways

Translation machinery is responsible for the production of cellular proteins; thus, cells devote the majority of their resources to ribosome biogenesis and protein synthesis. Single-copy loss of function in the translation machinery components results in rare ribosomopathy disorders, such as Diamond-Blackfan anaemia in humans and similar developmental defects in various model organisms. Somatic copy number alterations of translation machinery components are also observed in specific tumours. The organism-wide response to haploinsufficient loss-of-function mutations in ribosomal proteins or translation machinery components is complex: variations in translation machinery lead to reduced ribosome biogenesis, protein translation and altered protein homeostasis and cellular signalling pathways. Cells are affected both autonomously and non-autonomously by changes in translation machinery or ribosome biogenesis through cell-cell interactions and secreted hormones. We first briefly introduce the model organisms where mutants or knockdowns of protein synthesis and ribosome biogenesis are characterized. Next, we specifically describe observations in Caenorhabditis elegans and Drosophila melanogaster, where insufficient protein synthesis in a subset of cells triggers cell non-autonomous growth or apoptosis responses that affect nearby cells and tissues. We then cover the characterized signalling pathways that interact with ribosome biogenesis/protein synthesis machinery with an emphasis on their respective functions during organism development.

On the origin of metastases: Induction of pro-metastatic states after impending cell death via ER stress, reprogramming, and a cytokine storm

How metastatic cells arise is unclear. Here, we search for the induction of recently characterized pro-metastatic states as a surrogate for the origin of metastasis. Since cell-death-inducing therapies can paradoxically promote metastasis, we ask if such treatments induce pro-metastatic states in human colon cancer cells. We find that post-near-death cells acquire pro-metastatic states (PAMEs) and form distant metastases in vivo. These PAME ("let's go" in Greek) cells exhibit a multifactorial cytokine storm as well as signs of enhanced endoplasmic reticulum (ER) stress and nuclear reprogramming, requiring CXCL8, INSL4, IL32, PERK-CHOP, and NANOG. PAMEs induce neighboring tumor cells to become PAME-induced migratory cells (PIMs): highly migratory cells that re-enact the storm and enhance PAME migration. Metastases are thus proposed to originate from the induction of pro-metastatic states through intrinsic and extrinsic cues in a pro-metastatic tumoral ecosystem, driven by an impending cell-death experience involving ER stress modulation, metastatic reprogramming, and paracrine recruitment via a cytokine storm.

Infection of Galleria mellonella (Lepidoptera) Larvae With the Entomopathogenic Fungus Conidiobolus coronatus (Entomophthorales) Induces Apoptosis of Hemocytes and Affects the Concentration of Eicosanoids in the Hemolymph

Apoptosis and autophagy, the mechanisms of programmed cell death, play critical roles in physiological and pathological processes in both vertebrates and invertebrates. Apoptosis is also known to play an important role in the immune response, particularly in the context of entomopathogenic infection. Of the factors influencing the apoptotic process during infection, two of the lesser known groups are caspases and eicosanoids. The aim of this study was to determine whether infection by the entomopathogenic soil fungus Conidiobolus coronatus is associated with apoptosis and changes in caspase activity in the hemocytes of Galleria mellonella larvae, and to confirm whether fungal infection may affect eicosanoid levels in the host. Larvae were exposed for 24 h to fully grown and sporulating fungus. Hemolymph was collected either immediately after termination of exposure (F24 group) or 24 h later (F48 group). Apoptosis/necrosis tests were performed in hemocytes using fluorescence microscopy and flow cytometry, while ELISA tests were used to measure eicosanoid levels. Apoptosis and necrosis occurred to the same degree in F24, but necrosis predominated in F48. Fungal infection resulted in caspase activation, increased PGE1, PGE2, PGA1, PGF2α, and 8-iso-PGF2α levels and decreased TXB2 levels, but had no effect on TXA2 or 11-dehydro-TXB2 concentrations. In addition, infected larvae demonstrated significantly increased PLA2 activity, known to be involved in eicosanoid biosynthesis. Our findings indicate that fungal infection simultaneously induces apoptosis in insects and stimulates general caspase activity, and this may be correlated with changes in the concentrations of eicosanoids.

The role of the tendon ECM in mechanotransduction: disruption and repair following overuse

Purpose: Tendon overuse injuries are prevalent conditions with limited therapeutic options to halt disease progression. The specialized extracellular matrix (ECM) both enables joint function and mediates mechanical signals to tendon cells, driving biological responses to exercise or injury. With overuse, tendon ECM composition and structure changes at multiple scales, disrupting mechanotransduction and resulting in inadequate repair and disease progression. This review highlights the multiscale ECM changes that occur with tendon overuse and corresponding effects on cell-matrix interactions and cellular response to load.Results: Different functional joint requirements and tendon types experience a wide range of loading profiles, creating varied downstream mechanical stimuli. Distinct ECM structure and mechanical properties within the fascicle matrix, interfascicle matrix, and enthesis and their varied disruption with overuse are considered. The pericellular matrix (PCM) comprising the microscale tendon cell environment has a unique composition that changes with overuse injury and exercise, suggesting an important role in mechanotransduction and promoting repair. Cell-matrix interactions are mediated by structures including cilia, integrins, connexins and cytoskeleton that signal downstream homeostasis, adaptation, or repair. ECM disruption with tendon overuse may cause altered mechanical loading and cell-matrix interactions, resulting in mechanobiological understimulation, apoptosis, and ineffective repair. Current interventions to promote repair of tendon overuse injuries including exercise, targeting cell signaling, and modulating inflammation are considered.Conclusion: Future therapeutics should be assessed with regard of their effects on multiscale mechanotransduction in addition to joint function, with consideration of the central role of ECM.

JNK Mediates Differentiation, Cell Polarity and Apoptosis During Amphioxus Development by Regulating Actin Cytoskeleton Dynamics and ERK Signalling

c-Jun N-terminal kinase (JNK) is a multi-functional protein involved in a diverse array of context-dependent processes, including apoptosis, cell cycle regulation, adhesion, and differentiation. It is integral to several signalling cascades, notably downstream of non-canonical Wnt and mitogen activated protein kinase (MAPK) signalling pathways. As such, it is a key regulator of cellular behaviour and patterning during embryonic development across the animal kingdom. The cephalochordate amphioxus is an invertebrate chordate model system straddling the invertebrate to vertebrate transition and is thus ideally suited for comparative studies of morphogenesis. However, next to nothing is known about JNK signalling or cellular processes in this lineage. Pharmacological inhibition of JNK signalling using SP600125 during embryonic development arrests gastrula invagination and causes convergence extension-like defects in axial elongation, particularly of the notochord. Pharynx formation and anterior oral mesoderm derivatives like the preoral pit are also affected. This is accompanied by tissue-specific transcriptional changes, including reduced expression of six3/6 and wnt2 in the notochord, and ectopic wnt11 in neurulating embryos treated at late gastrula stages. Cellular delamination results in accumulation of cells in the gut cavity and a dorsal fin-like protrusion, followed by secondary Caspase-3-mediated apoptosis of polarity-deficient cells, a phenotype only partly rescued by co-culture with the pan-Caspase inhibitor Z-VAD-fmk. Ectopic activation of extracellular signal regulated kinase (ERK) signalling in the neighbours of extruded notochord and neural cells, possibly due to altered adhesive and tensile properties, as well as defects in cellular migration, may explain some phenotypes caused by JNK inhibition. Overall, this study supports conserved functions of JNK signalling in mediating the complex balance between cell survival, apoptosis, differentiation, and cell fate specification during cephalochordate morphogenesis.

Distinct roles of Bendless in regulating FSC niche competition and daughter cell differentiation

A major goal in the study of adult stem cells is to understand how cell fates are specified at the proper time and place to facilitate tissue homeostasis. Here, we found that an E2 ubiquitin ligase, Bendless (Ben), has multiple roles in the Drosophila ovarian epithelial follicle stem cell (FSC) lineage. First, Ben is part of the JNK signaling pathway, and we found that it, as well as other JNK pathway genes, are essential for differentiation of FSC daughter cells. Our data suggest that JNK signaling promotes differentiation by suppressing the activation of the EGFR effector, ERK. Also, we found that loss of ben, but not the JNK kinase hemipterous, resulted in an upregulation of hedgehog signaling, increased proliferation and increased niche competition. Lastly, we demonstrate that the hypercompetition phenotype caused by loss of ben is suppressed by decreasing the rate of proliferation or knockdown of the hedgehog pathway effector, Smoothened (Smo). Taken together, our findings reveal a new layer of regulation in which a single gene influences cell signaling at multiple stages of differentiation in the early FSC lineage.

Tumorigenesis and cell competition in Drosophila in the absence of polyhomeotic function

Cell competition is a homeostatic process that eliminates by apoptosis unfit or undesirable cells from animal tissues, including tumor cells that appear during the life of the organism. In Drosophila there is evidence that many types of oncogenic cells are eliminated by cell competition. One exception is cells mutant for polyhomeotic (ph), a member of the Polycomb family of genes; most of the isolated mutant ph clones survive and develop tumorous overgrowths in imaginal discs. To characterize the tumorigenic effect of the lack of ph, we first studied the growth of different regions of the wing disc deficient in ph activity and found that the effect is restricted to the proximal appendage. Moreover, we found that ph-deficient tissue is partially refractory to apoptosis. Second, we analyzed the behavior of clones lacking ph function and found that many suffer cell competition but are not completely eliminated. Unexpectedly, we found that nonmutant cells also undergo cell competition when surrounded by ph-deficient cells, indicating that within the same tissue cell competition may operate in opposite directions. We suggest two reasons for the incompleteness of cell competition in ph mutant cells: 1) These cells are partially refractory to apoptosis, and 2) the loss of ph function alters the identity of imaginal cells and subsequently their cell affinities. It compromises the winner/loser interaction, a prerequisite for cell competition.

Necrosis-induced apoptosis promotes regeneration in Drosophila wing imaginal discs

Regeneration is a complex process that requires a coordinated genetic response to tissue loss. Signals from dying cells are crucial to this process and are best understood in the context of regeneration following programmed cell death, like apoptosis. Conversely, regeneration following unregulated forms of death, such as necrosis, have yet to be fully explored. Here, we have developed a method to investigate regeneration following necrosis using the Drosophila wing imaginal disc. We show that necrosis stimulates regeneration at an equivalent level to that of apoptosis-mediated cell death and activates a similar response at the wound edge involving localized JNK signaling. Unexpectedly, however, necrosis also results in significant apoptosis far from the site of ablation, which we have termed necrosis-induced apoptosis (NiA). This apoptosis occurs independent of changes at the wound edge and importantly does not rely on JNK signaling. Furthermore, we find that blocking NiA limits proliferation and subsequently inhibits regeneration, suggesting that tissues damaged by necrosis can activate programmed cell death at a distance from the injury to promote regeneration.

Downregulation of miR-223 promotes HMGB2 expression and induces oxidative stress to activate JNK and promote autophagy in an in vitro model of acute lung injury

BACKGROUND

Excessive autophagic activity in alveolar epithelial cells is one of the main causes of acute lung injury (ALI), but the underlying molecular mechanism has not been fully elucidated. Previous studies have shown that microRNAs (miRs) are involved in regulating autophagy in several diseases. This study aimed to determine the role of miR-223 in excessive autophagic activity in alveolar epithelial cells and the underlying mechanism to identify a novel therapeutic targets for the development of new drugs to treat acute respiratory distress syndrome (ARDS).

METHODS

A549 cells were treated with lipopolysaccharide (LPS) to establish an ALI in vitro model. The expression of miR-223 and its role of miR-223 in regulating oxidative stress and autophagy in the LPS-treated A549 cells, were examined using RT-PCR, flow cytometry and ELISA. A luciferase reporter assay was performed to verify the interaction between miR-223 and the high-mobility group box 2 (HMGB2) protein.

RESULTS

The results showed that the LPS treatment downregulated miR-223 expression in alveolar epithelial cells. We further proved that miR-223 directly targeted the 3-untranslated region of the HMGB2 gene and the downregulation of miR-223 increased HMGB2 protein level, which activated the JNK signalling pathway and thus induced oxidative stress and autophagy in LPS-treated alveolar epithelial cells. Knockdown of HMGB2 protein deactivated the JNK signalling pathway and inhibited autophagy and oxidative stress in alveolar epithelial cells.

CONCLUSIONS

The results of this study suggest that miR-223 regulates oxidative stress and autophagy in alveolar epithelial cells by targeting HMGB2 via the JNK signalling pathway.

An Open Question: Is Non-Ionizing Radiation a Tool for Controlling Apoptosis-Induced Proliferation?

Non-ionizing radiation is commonly used in the clinical setting, despite its known ability to trigger oxidative stress and apoptosis, which can lead to damage and cell death. Although induction of cell death is typically considered harmful, apoptosis can also be beneficial in the right context. For example, cell death can serve as the signal for new tissue growth, such as in apoptosis-induced proliferation. Recent data has shown that exposure to non-ionizing radiation (such as weak static magnetic fields, weak radiofrequency magnetic fields, and weak electromagnetic fields) is able to modulate proliferation, both in cell culture and in living organisms (for example during tissue regeneration). This occurs via in vivo changes in the levels of reactive oxygen species (ROS), which are canonical activators of apoptosis. This review will describe the literature that highlights the tantalizing possibility that non-ionizing radiation could be used to manipulate apoptosis-induced proliferation to either promote growth (for regenerative medicine) or inhibit it (for cancer therapies). However, as uncontrolled growth can lead to tumorigenesis, much more research into this exciting and developing area is needed in order to realize its promise.

JNK Signaling in Drosophila Aging and Longevity

The evolutionarily conserved c-Jun N-terminal kinase (JNK) signaling pathway is a critical genetic determinant in the control of longevity. In response to extrinsic and intrinsic stresses, JNK signaling is activated to protect cells from stress damage and promote survival. In Drosophila, global JNK upregulation can delay aging and extend lifespan, whereas tissue/organ-specific manipulation of JNK signaling impacts lifespan in a context-dependent manner. In this review, focusing on several tissues/organs that are highly associated with age-related diseases-including metabolic organs (intestine and fat body), neurons, and muscles-we summarize the distinct effects of tissue/organ-specific JNK signaling on aging and lifespan. We also highlight recent progress in elucidating the molecular mechanisms underlying the tissue-specific effects of JNK activity. Together, these studies highlight an important and comprehensive role for JNK signaling in the regulation of longevity in Drosophila.

Relish plays a dynamic role in the niche to modulate Drosophila blood progenitor homeostasis in development and infection

Immune challenges demand the gearing up of basal hematopoiesis to combat infection. Little is known about how during development, this switch is achieved to take care of the insult. Here, we show that the hematopoietic niche of the larval lymph gland of Drosophila senses immune challenge and reacts to it quickly through the nuclear factor-κB (NF-κB), Relish, a component of the immune deficiency (Imd) pathway. During development, Relish is triggered by ecdysone signaling in the hematopoietic niche to maintain the blood progenitors. Loss of Relish causes an alteration in the cytoskeletal architecture of the niche cells in a Jun Kinase-dependent manner, resulting in the trapping of Hh implicated in progenitor maintenance. Notably, during infection, downregulation of Relish in the niche tilts the maintenance program toward precocious differentiation, thereby bolstering the cellular arm of the immune response.

Cell competition from development to neurodegeneration

Cell competition is a process by which suboptimal cells are eliminated to the benefit of cells with higher fitness. It is a surveillance mechanism that senses differences in the fitness status by several modes, such as expression of fitness fingerprints, survival factor uptake rate and resistance to mechanical stress. Fitness fingerprints-mediated cell competition recognizes isoforms of the transmembrane protein Flower, and translates the relative fitness of cells into distinct fates through the Flower code. Impairments in cell competition potentiate the development of diseases like cancer and ageing-related pathologies. In cancer, malignant cells acquire a supercompetitor behaviour, killing the neighbouring cells and overtaking the tissue, thus avoiding elimination. Neurodegenerative disorders affect millions of people and are characterized by cognitive decline and locomotor deficits. Alzheimer's disease is the most common form of dementia, and one of the largely studied diseases. However, the cellular processes taking place remain unclear. Drosophila melanogaster is an emerging neurodegeneration model due to its versatility as a tool for genetic studies. Research in a Drosophila Alzheimer's disease model detected fitness markers in the suboptimal and hyperactive neurons, thus establishing a link between cell competition and Alzheimer's disease. In this Review, we overview cell competition and the new insights related to neurodegenerative disorders, and discuss how research in the field might contribute to the development of new therapeutic targets for these diseases.

Acute exposure to fipronil induces oxidative stress, apoptosis and impairs epithelial homeostasis in the midgut of the stingless bee Partamona helleri Friese (Hymenoptera: Apidae)

Partamona helleri is an important pollinator in natural and agricultural ecosystems in the neotropics. However, the foraging activity of this bee increases its risk of exposure to pesticides, which may affect both the individuals and the colony. Thus, this study aims to evaluate the side effects of LC₅₀ of fipronil (0.28 ng a.i. μL^-1) on the midgut morphology, antioxidant activity and some pathways of cell death, proliferation and differentiation in workers of P. helleri, after 24 h of oral exposure. Fipronil caused morphological alterations in the midgut of the bees. The activities of the detoxification enzymes superoxide dismutase, catalase and glutathione S-transferase increased after exposure, which suggests the occurrence of a detoxification mechanism. Furthermore, exposure to fipronil changed the number of positive cells for signaling-pathway proteins in the midgut of bees, which indicates the induction of cell death by the apoptotic pathway and impairment of the midgut epithelial regeneration. These results demonstrate that fipronil may negatively affect the morphology and physiology of the midgut of the stingless bee P. helleri and impose a threat to the survival of non-target organisms.

A novel injury paradigm in the central nervous system of adult Drosophila: molecular, cellular and functional aspects

The mammalian central nervous system (CNS) exhibits limited regenerative capacity and the mechanisms that mediate its regeneration are not fully understood. Here, we present a novel experimental design to damage the CNS by using a contusion injury paradigm. The design of this protocol allows the study of long-term and short-term cellular responses, including those of the CNS and the immune system, and of any implications regarding functional recovery. We demonstrate for the first time that adult Drosophilamelanogaster glial cells undergo spontaneous functional recovery following crush injury. This crush injury leads to an intermediate level of functional recovery after damage, which is ideal to screen for genes that facilitate or prevent the regeneration process. Here, we validate this model and analyse the immune responses of glial cells as a central regulator of functional regeneration. Additionally, we demonstrate that glial cells and macrophages contribute to functional regeneration through mechanisms involving the Jun N-terminal kinase (JNK) pathway and the Drosophila protein Draper (Drpr), characteristic of other neural injury paradigms. We show that macrophages are recruited to the injury site and are required for functional recovery. Further, we show that the proteins Grindelwald and Drpr in Drosophila glial cells mediate activation of JNK, and that expression of drpr is dependent on JNK activation. Finally, we link neuron-glial communication and the requirement of neuronal vesicular transport to regulation of the JNK pathway and functional recovery.

This article has an associated First Person interview with the first author of the paper.

Summary: Central nervous system crush injury paradigm in adult Drosophilamelanogaster is a suitable model to study the cellular events, and genetic pathways behind injury responses and functional regeneration. We describe the immune responses of glial cells, neurons and macrophages following injury, and the functional relevance of each response.

Serial single-cell genomics reveals convergent subclonal evolution of resistance as early-stage breast cancer patients progress on endocrine plus CDK4/6 therapy

Combining cyclin-dependent kinase (CDK) inhibitors with endocrine therapy improves outcomes for metastatic estrogen receptor positive (ER+) breast cancer patients but its value in earlier stage patients is unclear. We examined evolutionary trajectories of early-stage breast cancer tumors, using single cell RNA sequencing (scRNAseq) of serial biopsies from the FELINE clinical trial (#NCT02712723) of endocrine therapy (letrozole) alone or combined with the CDK inhibitor ribociclib. Despite differences in subclonal diversity evolution across patients and treatments, common resistance phenotypes emerged. Resistant tumors treated with combination therapy showed accelerated loss of estrogen signaling with convergent up-regulation of JNK signaling through growth factor receptors. In contrast, cancer cells maintaining estrogen signaling during mono- or combination therapy showed potentiation of CDK4/6 activation and ERK upregulation through ERBB4 signaling. These results indicate that combination therapy in early-stage ER+ breast cancer leads to emergence of resistance through a shift from estrogen to alternative growth signal-mediated proliferation.

The Emerging Roles of JNK Signaling in Drosophila Stem Cell Homeostasis

The Jun N-terminal kinase (JNK) pathway is an evolutionary conserved kinase cascade best known for its roles during stress-induced apoptosis and tumor progression. Recent findings, however, have identified new roles for this pleiotropic pathway in stem cells during regenerative responses and in cellular plasticity. Here, we provide an overview of recent findings about the new roles of JNK signaling in stem cell biology using two well-established Drosophila models: the testis and the intestine. We highlight the pathway’s roles in processes such as proliferation, death, self-renewal and reprogramming, and discuss the known parallels between flies and mammals.

Nutrition and PI3K/Akt signaling are required for p38-dependent regeneration

Regeneration after damage requires early signals to trigger the tissue repair machinery. Reactive oxygen species (ROS) act as early signals that are sensed by the MAP3 kinase Ask1, which in turn activates by phosphorylation the MAP kinases p38 and JNK. The sustained or high activation of these kinases can result in apoptosis, whereas short or low activation can promote regeneration. Using the Ask1-dependent regeneration program, we demonstrate in Drosophila wing that PI3K/Akt signaling is necessary for Ask1 to activate p38, but not JNK. In addition, nutrient restriction or mutations that target Ser83 of the Drosophila Ask1 protein, a PI3K/Akt-sensitive residue, block regeneration. However, these effects can be reversed by the ectopic activation of p38, but not of JNK. Our results demonstrate that Ask1 controls the activation of p38 through Ser83, and that the phosphorylation of p38 during regeneration is nutrient sensitive. This mechanism is important for discriminating between p38 and JNK in the cells involved in tissue repair and regenerative growth.

Adiponectin and Thyroid Cancer: Insight into the Association between Adiponectin and Obesity

In recent decades, the incidence and diagnosis of thyroid cancer have risen dramatically, and thyroid cancer has now become the most common endocrine cancer in the world. The onset of thyroid cancer is insidious, and its progression is slow and difficult to detect. Therefore, early prevention and treatment have important strategic significance. Moreover, an in-depth exploration of the pathogenesis of thyroid cancer is key to early prevention and treatment. Substantial evidence supports obesity as an independent risk factor for thyroid cancer. Adipose tissue dysfunction in the obese state is accompanied by dysregulation of a variety of adipocytokines. Adiponectin (APN) is one of the most pivotal adipocytokines, and its connection with obesity and obesity-related disease has gradually become a hot topic in research. Recently, the association between APN and thyroid cancer has received increasing attention. The purpose of this review is to systematically review previous studies, give prominence to APN, focus on the relationship between APN, obesity and thyroid cancer, and uncover the underlying pathogenic mechanisms.

Cell competition: A historical perspective

Cell competition is a homeostatic process designed to remove from animal tissues viable cells that are unfit, abnormal or malignant and that may compromise the general fitness or the viability of the organism. Originally discovered in Drosophila in the mid-seventies of last century, there is strong evidence that it also occurs in other metazoans, where cell competition appears to play a similar surveillance role. In this review I summarize the field of cell competition, with special emphasis in the history of the phenomenon within the general frame of Developmental Biology in the second half of the XX century, pointing out the key observations and the evolution of ideas that have led to the current understanding.

Targeting the MDSCs of Tumors In Situ With Inhibitors of the MAPK Signaling Pathway to Promote Tumor Regression

Myeloid-derived suppressor cells (MDSCs) are one of the major components of the tumor microenvironment. Evidence has shown differences in the functions and fates of MDSCs in the tumor tissue and the periphery. However, the exact mechanism that regulates MDSC function has not been completely clarified. In this study, we performed RNA sequencing of MDSCs derived from the spleen and tumor. Based on the results of our RNA-seq analysis, mitogen-activated protein kinases (MAPK) were significantly increased in tumor polymorphonuclear MDSCs (PMN-MDSCs) and monocytic MDSCs (M-MDSCs). Subsequently, 3 major MAPK pathways, including extracellular signal-regulated protein kinases (ERK), p38 and c-Jun NH2-terminal kinases (JNK), were studied to analyze the role of MAPKs in MDSCs. The ERK 1/2 inhibitor SCH772984 and the JNK inhibitor SP600125 significantly increased the apoptosis of both PMN-MDSCs and M-MDSCs in vitro. In addition, SCH772984 exerted a strong effect on inhibiting tumor growth. The flow cytometry analysis showed significant increases in the ratio of M1:M2 tumor-associated macrophages, meanwhile the number of CD4⁺, CD8⁺, CD4⁺CD69⁺ and CD8⁺CD69⁺ lymphocytes were increased after SCH772984 treatment. Our findings established the effect of MAPKs on the tumor microenvironment via MDSCs and may facilitate the development of new antitumor strategies.

Zfh-2 facilitates Notch-induced apoptosis in the CNS and appendages of Drosophila melanogaster

Apoptosis is a fundamental remodeling process for most tissues during development. In this manuscript we examine a pro-apoptotic function for the Drosophila DNA binding protein Zfh-2 during development of the central nervous system (CNS) and appendages. In the CNS we find that a loss-of-function zfh-2 allele gives an overall reduction of apoptotic cells in the CNS, and an altered pattern of expression for the axonal markers 22C10 and FasII. This same loss-of-function zfh-2 allele causes specific cells in the NB7-3 lineage of the CNS that would normally undergo apoptosis to be inappropriately maintained, whereas a gain-of-function zfh-2 allele has the opposite effect, resulting in a loss of normal NB 7-3 progeny. We also demonstrate that Zfh-2 and Hunchback reciprocally repress each other's gene expression which limits apoptosis to later born progeny of the NB7-3 lineage. Apoptosis is also required for proper segmentation of the fly appendages. We find that Zfh-2 co-localizes with apoptotic cells in the folds of the imaginal discs and presumptive cuticular joints. A reduction of Zfh-2 levels with RNAi inhibits expression of the pro-apoptotic gene reaper, and produces abnormal joints in the leg, antenna and haltere. Apoptosis has previously been shown to be activated by Notch signaling in both the NB7-3 CNS lineage and the appendage joints. Our results indicate that Zfh-2 facilitates Notch-induced apoptosis in these structures.

Drosophila as a Model for Infectious Diseases

The fruit fly, Drosophila melanogaster, has been used to understand fundamental principles of genetics and biology for over a century. Drosophila is now also considered an essential tool to study mechanisms underlying numerous human genetic diseases. In this review, we will discuss how flies can be used to deepen our knowledge of infectious disease mechanisms in vivo. Flies make effective and applicable models for studying host-pathogen interactions thanks to their highly conserved innate immune systems and cellular processes commonly hijacked by pathogens. Drosophila researchers also possess the most powerful, rapid, and versatile tools for genetic manipulation in multicellular organisms. This allows for robust experiments in which specific pathogenic proteins can be expressed either one at a time or in conjunction with each other to dissect the molecular functions of each virulent factor in a cell-type-specific manner. Well documented phenotypes allow large genetic and pharmacological screens to be performed with relative ease using huge collections of mutant and transgenic strains that are publicly available. These factors combine to make Drosophila a powerful tool for dissecting out host-pathogen interactions as well as a tool to better understand how we can treat infectious diseases that pose risks to public health, including COVID-19, caused by SARS-CoV-2.

Knockdown of nrf2 Exacerbates TNF-α-Induced Proliferation and Invasion of Rheumatoid Arthritis Fibroblast-Like Synoviocytes through Activating JNK Pathway

Fibroblast-like synoviocytes (FLS) in the synovial tissue of rheumatoid arthritis (RA) exhibit over-proliferative and aggressive phenotypes, which participate in the pathophysiology of RA. In RA, little is known about the nonantioxidant effect of nuclear factor erythroid 2-related factor 2 (nrf2), the master regulator of redox homeostasis. In this study, we aimed to explore the expression and upstream regulatory factors of nrf2 and revealed its functions in modulating the proliferation and invasion in RA-FLS. FLS were isolated from RA and osteoarthritis patients. Expression of nrf2 in the synovial tissues and FLS was analyzed by immunohistochemistry, real-time PCR, Western blotting, and immunofluorescence staining. Cell proliferation was examined by Cell Counting Kit-8. Cell invasion was tested by transwell assay. Phosphorylation of JNK was determined by Western blotting. The results showed that nrf2 expression in the RA synovial tissues was upregulated. TNF-α promoted expression and nuclear translocation of nrf2 in RA-FLS and increased the intracellular reactive oxygen species (ROS) level. Nrf2 nuclear translocation was blocked by ROS inhibitor N-acetylcysteine. Both knockdown of nrf2 by siRNA and inhibition of nrf2 by ML385 significantly promoted the TNF-α-induced proliferation and invasion of RA-FLS. Activation of nrf2 by sulforaphane (SFN) profoundly inhibited the TNF-α-induced proliferation and invasion of RA-FLS. Knockdown of nrf2 also enhanced the TNF-α-induced matrix metalloproteinases (MMPs) expression and phosphorylation of JNK in RA-FLS. Proliferation and invasion of RA-FLS incubated with TNF-α and nrf2 siRNA were inhibited by pretreatment with JNK inhibitor SP600125. In conclusion, nrf2 is overexpressed in synovial tissues of RA patients, which may be promoted by TNF-α and ROS levels. Activation of nrf2 may suppress TNF-α-induced proliferation, invasion, and MMPs expression in RA-FLS by inhibiting JNK activation, indicating that nrf2 plays a protective role in relieving the severity of synovitis in RA. Our results might provide novel insights into the treatment of RA.

Deltex cooperates with TRAF6 to promote apoptosis and cell migration through Eiger-independent JNK activation in Drosophila

JNK signaling is a highly conserved signaling pathway that regulates a broad spectrum of cellular processes including cell proliferation, migration, and apoptosis. In Drosophila, JNK signaling is activated by binding of the tumor necrosis factor (TNF) Eiger to its receptor Wengen, and a conserved signaling cascade operates that culminates into activation of dual phosphatase Puckered thereby triggering apoptosis. The tumor necrosis factor receptor (TNFR) associated factor 6 (TRAF6) is an adaptor protein, which transduces the signal from TNFRs and Toll-like receptor/interleukin-1 receptor superfamily to induce a wide spectrum of cellular responses. TRAF6 also acts as the adaptor protein that mediates Eiger/JNK signaling in Drosophila. In a genetic interaction study, deltex (Dx) was identified as a novel interactor of TRAF6. Dx is well known to regulate Notch signaling in a context-dependent manner. Our data suggest that combinatorial action of Dx and TRAF6 enhances the Dx-induced wing nicking phenotype by inducing caspase-mediated cell death. Co-expression of Dx and TRAF6 also results in enhanced invasive behavior and perturbs the normal morphology of cells. The cooperative action of Dx and TRAF6 is attributed to JNK activation, which also leads to ectopic wingless (Wg) and decapentaplegic (Dpp) expression. Our results also reveal that the endocytic pathway component Rab7 may play a pivotal role in the regulation of Dx-TRAF6-mediated activation of JNK signaling. Here, we present the fact that Dx and TRAF6 together activate JNK signaling in an Eiger-independent mechanism.

Mud Loss Restricts Yki-Dependent Hyperplasia in Drosophila Epithelia

Tissue development demands precise control of cell proliferation and organization, which is achieved through multiple conserved signaling pathways and protein complexes in multicellular animals. Epithelia are a ubiquitous tissue type that provide diverse functions including physical protection, barrier formation, chemical exchange, and secretory activity. However, epithelial cells are also a common driver of tumorigenesis; thus, understanding the molecular mechanisms that control their growth dynamics is important in understanding not only developmental mechanisms but also disease. One prominent pathway that regulates epithelial growth is the conserved Hippo/Warts/Yorkie network. Hippo/Warts inactivation, or activating mutations in Yorkie that prevent its phosphorylation (e.g., YkiS168A), drive hyperplastic tissue growth. We recently reported that loss of Mushroom body defect (Mud), a microtubule-associated protein that contributes to mitotic spindle function, restricts YkiS168A-mediated growth in Drosophila imaginal wing disc epithelia. Here we show that Mud loss alters cell cycle progression and triggers apoptosis with accompanying Jun kinase (JNK) activation in YkiS168A-expressing discs. To identify additional molecular insights, we performed RNAseq and differential gene expression profiling. This analysis revealed that Mud knockdown in YkiS168A-expressing discs resulted in a significant downregulation in expression of core basement membrane (BM) and extracellular matrix (ECM) genes, including the type IV collagen gene viking. Furthermore, we found that YkiS168A-expressing discs accumulated increased collagen protein, which was reduced following Mud knockdown. Our results suggest that ECM/BM remodeling can limit untoward growth initiated by an important driver of tumor growth and highlight a potential regulatory link with cytoskeleton-associated genes.

Identification of the Wallenda JNKKK as an Alk suppressor reveals increased competitiveness of Alk-expressing cells

Anaplastic lymphoma kinase (Alk) is a receptor tyrosine kinase of the insulin receptor super-family that functions as oncogenic driver in a range of human cancers such as neuroblastoma. In order to investigate mechanisms underlying Alk oncogenic signaling, we conducted a genetic suppressor screen in Drosophila melanogaster. Our screen identified multiple loci important for Alk signaling, including members of Ras/Raf/ERK-, Pi3K-, and STAT-pathways as well as tailless (tll) and foxo whose orthologues NR2E1/TLX and FOXO3 are transcription factors implicated in human neuroblastoma. Many of the identified suppressors were also able to modulate signaling output from activated oncogenic variants of human ALK, suggesting that our screen identified targets likely relevant in a wide range of contexts. Interestingly, two misexpression alleles of wallenda (wnd, encoding a leucine zipper bearing kinase similar to human DLK and LZK) were among the strongest suppressors. We show that Alk expression leads to a growth advantage and induces cell death in surrounding cells. Our results suggest that Alk activity conveys a competitive advantage to cells, which can be reversed by over-expression of the JNK kinase kinase Wnd.

Rounding up the Usual Suspects: Assessing Yorkie, AP-1, and Stat Coactivation in Tumorigenesis

Can hyperactivation of a few key signaling effectors be the underlying reason for the majority of epithelial cancers despite different driver mutations? Here, to address this question, we use the Drosophila model, which allows analysis of gene expression from tumors with known initiating mutations. Furthermore, its simplified signaling pathways have numerous well characterized targets we can use as pathway readouts. In Drosophila tumor models, changes in the activities of three pathways, Jun N-terminal Kinase (JNK), Janus Kinase / Signal Transducer and Activator of Transcription (JAK/STAT), and Hippo, mediated by AP-1 factors, Stat92E, and Yorkie, are reported frequently. We hypothesized this may indicate that these three pathways are commonly deregulated in tumors. To assess this, we mined the available transcriptomic data and evaluated the activity levels of eight pathways in various tumor models. Indeed, at least two out of our three suspects contribute to tumor development in all Drosophila cancer models assessed, despite different initiating mutations or tissues of origin. Surprisingly, we found that Notch signaling is also globally activated in all models examined. We propose that these four pathways, JNK, JAK/STAT, Hippo, and Notch, are paid special attention and assayed for systematically in existing and newly developed models.

JNK signaling in Drosophila immunity and homeostasis

As members of the mitogen-activated protein kinase (MAPK) family, the c-Jun N-terminal kinases (JNKs) regulate cell responses to a wide range of extrinsic and intrinsic insults, including irradiation, reactive oxygen species (ROS), DNA damage, heat, bacterial antigens, and inflammatory cytokines. Particularly, JNK signaling regulates and promotes many important physiological processes that influence metabolic and tissue homeostasis, cell death/survival, and cell damage repair and ultimately impacts the lifespan of an organism. This diverse functionality causes a variety of tissue-specific and context-specific cellular responses, mediated by various cross talks between JNK and other cellular signaling pathways. Thus, highlighting its significance as a determinant of stress responses, JNK loss-of-function mutations have been implicated in a multitude of pathologies, including neurodegenerative diseases, diabetes, and cancer. Because JNK functions are specified in a context-dependent manner and can greatly vary, the underlying causes for these different outcomes remain largely unresolved despite the gained knowledge of many regulatory roles of JNK signaling during the past two decades. In Drosophila melanogaster, JNK signaling is conserved and required for immune responses, as well as the development for morphogenetic processes (embryonic dorsal closure and thorax closure). Therefore, Drosophila innate immunity provides the ideal model to understand the complex mechanisms underlying JNK activation and regulation. In the following, we review studies in Drosophila that highlight several mechanisms by which JNK signaling influences immunity and homeostasis.