Dissecting social cell biology and tumors using Drosophila genetics

Chicken skin-derived collagen peptides chelated zinc promotes zinc absorption and represses tumor growth and invasion in vivo by suppressing autophagy

To improve the utilization value of chicken by-products, we utilized the method of step-by-step hydrolysis with bromelain and flavourzyme to prepare low molecular weight chicken skin collagen peptides (CCP) (<5 kDa) and characterized the amino acids composition of the CCP. Then, we prepared novel CCP-chelated zinc (CCP–Zn) by chelating the CCP with ZnSO₄. We found that the bioavailability of CCP–Zn is higher than ZnSO₄. Besides, CCP, ZnSO₄, or CCP–Zn effectively repressed the tumor growth, invasion, and migration in a Drosophila malignant tumor model. Moreover, the anti-tumor activity of CCP–Zn is higher than CCP or ZnSO₄. Furthermore, the functional mechanism studies indicated that CCP, ZnSO₄, or CCP–Zn inhibits tumor progression by reducing the autonomous and non-autonomous autophagy in tumor cells and the microenvironment. Therefore, this research provides in vivo evidence for utilizing chicken skin in the development of zinc supplements and cancer treatment in the future.

Intrinsic and damage-induced JAK/STAT signaling regulate developmental timing by the Drosophila prothoracic gland

Development involves tightly paced, reproducible sequences of events, yet it must adjust to conditions external to it, such as resource availability and organismal damage. A major mediator of damage-induced immune responses in vertebrates and insects is JAK/STAT signaling. At the same time, JAK/STAT activation by the Drosophila Upd cytokines is pleiotropically involved in normal development of multiple organs. Whether inflammatory and developmental JAK/STAT roles intersect is unknown. Here, we show that JAK/STAT is active during development of the prothoracic gland (PG), which controls metamorphosis onset through ecdysone production. Reducing JAK/STAT signaling decreased PG size and advanced metamorphosis. Conversely, JAK/STAT hyperactivation by overexpression of pathway components or SUMOylation loss caused PG hypertrophy and metamorphosis delay. Tissue damage and tumors, known to secrete Upd cytokines, also activated JAK/STAT in the PG and delayed metamorphosis, at least in part by inducing expression of the JAK/STAT target Apontic. JAK/STAT damage signaling, therefore, regulates metamorphosis onset by co-opting its developmental role in the PG. Our findings in Drosophila provide insights on how systemic effects of damage and cancer can interfere with hormonally controlled development and developmental transitions.

Summary: Damage signaling from tumors mediated by JAK/STAT-activating Upd cytokines delays the Drosophila larva–pupa transition through co-option of a JAK/STAT developmental role in the prothoracic gland.

Drosophila as a model for chromosomal instability

Chromosomal instability (CIN) is a common feature of tumours that leads to increased genetic diversity in the tumour and poor clinical outcomes. There is considerable interest in understanding how CIN comes about and how its contribution to drug resistance and metastasis might be counteracted. In the last decade a number of CIN model systems have been developed in Drosophila that offer unique benefits both in understanding the development of CIN in a live animal as well as giving the potential to do genome wide screens for therapeutic candidate genes. This review outlines the mechanisms used in several Drosophila CIN model systems and summarizes some significant outcomes and opportunities that they have produced.

Context-dependent interplay between Hippo and JNK pathway in Drosophila

Both Hippo and JNK signaling have well-established roles in regulating many physiological processes, including cell proliferation, growth, survival, and migration. An increasing body of evidence shows that dysregulation of either Hippo or JNK pathway would lead to tumorigenesis. Recently, studies in Drosophila has coupled Hippo with JNK pathway in numerous ways ranging from tissue regeneration to growth control. In this review, I provide an overview of the current understanding of crosstalk between Hippo and JNK pathway in Drosophila, and discuss their context-dependent interactions in gut homeostasis, regeneration, cell competition and migration.

Misshapen Disruption Cooperates with RasV12 to Drive Tumorigenesis

Although RAS family genes play essential roles in tumorigenesis, effective treatments targeting RAS-related tumors are lacking, partly because of an incomplete understanding of the complex signaling crosstalk within RAS-related tumors. Here, we performed a large-scale genetic screen in Drosophila eye imaginal discs and identified Misshapen (Msn) as a tumor suppressor that synergizes with oncogenic Ras (Ras^V12) to induce c-Jun N-terminal kinase (JNK) activation and Hippo inactivation, then subsequently leads to tumor overgrowth and invasion. Moreover, ectopic Msn expression activates Hippo signaling pathway and suppresses Hippo signaling disruption-induced overgrowth. Importantly, we further found that Msn acts downstream of protocadherin Fat (Ft) to regulate Hippo signaling. Finally, we identified msn as a Yki/Sd target gene that regulates Hippo pathway in a negative feedback manner. Together, our findings identified Msn as a tumor suppressor and provide a novel insight into RAS-related tumorigenesis that may be relevant to human cancer biology.

ZnT7 RNAi favors RafGOFscrib-/--induced tumor growth and invasion in Drosophila through JNK signaling pathway

The disruption of zinc homeostasis has been identified in patients suffering from various cancers, but a causative relationship has not yet been established. Drosophila melanogaster has become a powerful model to study cancer biology. Here using a Drosophila model of malignant tumor Raf^GOFscrib^-/-, we observed that the tumor growth, invasion and migration were enhanced by silencing dZnT7, a zinc transporter localized on the Golgi apparatus. Further study indicated that the zinc deficiency in Golgi of dZnT7 RNAi resulted in ER stress which could activate the c-Jun-N-terminal Kinase (JNK) signaling and this process is mediated by Atg9. Lastly, we demonstrated that the exacerbation of dZnT7 RNAi on tumor was promoted by JNK signaling-dependent cell autonomous and non-autonomous autophagy. These findings suggest that zinc homeostasis in secretory compartments may provide a new therapeutic target for tumor treatment.

The Upd3 cytokine couples inflammation to maturation defects in Drosophila

Developmental transitions, such as puberty or metamorphosis, are tightly controlled by steroid hormones and can be delayed by the appearance of growth abnormalities, developmental tumors, or inflammatory disorders such as inflammatory bowel disease or cystic fibrosis.^1-4 Here, we used a highly inflammatory epithelial model of malignant transformation in Drosophila^5,6 to unravel the role of Upd3-a cytokine with homology to interleukin-6-and the JAK/STAT signaling pathway in coupling inflammation to a delay in metamorphosis. We present evidence that Upd3 produced by malignant and nearby cell populations signals to the prothoracic gland-an endocrine tissue primarily dedicated to the production of the steroid hormone ecdysone-to activate JAK/STAT and bantam microRNA (miRNA) and to delay metamorphosis. Upd cytokines produced by the tumor site contribute to increasing the systemic levels of Upd3 by amplifying its expression levels in a cell-autonomous manner and by inducing Upd3 expression in neighboring tissues in a non-autonomous manner, culminating in a major systemic response to prevent larvae from initiating pupa transition. Our results identify a new regulatory network impacting on ecdysone biosynthesis and provide new insights into the potential role of inflammatory cytokines and the JAK/STAT signaling pathway in coupling inflammation to delays in puberty.

Selective Killing of RAS-Malignant Tissues by Exploiting Oncogene-Induced DNA Damage

Several oncogenes induce untimely entry into S phase and alter replication timing and progression, thereby generating replicative stress, a well-known source of genomic instability and a hallmark of cancer. Using an epithelial model in Drosophila, we show that the RAS oncogene, which triggers G1/S transition, induces DNA damage and, at the same time, silences the DNA damage response pathway. RAS compromises ATR-mediated phosphorylation of the histone variant H2Av and ATR-mediated cell-cycle arrest in G2 and blocks, through ERK, Dp53-dependent induction of cell death. We found that ERK is also activated in normal tissues by an exogenous source of damage and that this activation is necessary to dampen the pro-apoptotic role of Dp53. We exploit the pro-survival role of ERK activation upon endogenous and exogenous sources of DNA damage to present evidence that its genetic or chemical inhibition can be used as a therapeutic opportunity to selectively eliminate RAS-malignant tissues.

MCF7 Spheroid Development: New Insight about Spatio/Temporal Arrangements of TNTs, Amyloid Fibrils, Cell Connections, and Cellular Bridges

Human breast adenocarcinoma cells (MCF7) grow in three-dimensional culture as spheroids that represent the structural complexity of avascular tumors. Therefore, spheroids offer a powerful tool for studying cancer development, aggressiveness, and drug resistance. Notwithstanding the large amount of data regarding the formation of MCF7 spheroids, a detailed description of the morpho-functional changes during their aggregation and maturation is still lacking. In this study, in addition to the already established role of gap junctions, we show evidence of tunneling nanotube (TNT) formation, amyloid fibril production, and opening of large stable cellular bridges, thus reporting the sequential events leading to MCF7 spheroid formation. The variation in cell phenotypes, sustained by dynamic expression of multiple proteins, leads to complex networking among cells similar to the sequence of morphogenetic steps occurring in embryogenesis/organogenesis. On the basis of the observation that early events in spheroid formation are strictly linked to the redox homeostasis, which in turn regulate amyloidogenesis, we show that the administration of N-acetyl-l-cysteine (NAC), a reactive oxygen species (ROS) scavenger that reduces the capability of cells to produce amyloid fibrils, significantly affects their ability to aggregate. Moreover, cells aggregation events, which exploit the intrinsic adhesiveness of amyloid fibrils, significantly decrease following the administration during the early aggregation phase of neutral endopeptidase (NEP), an amyloid degrading enzyme.

Effects of Xuefu Zhuyu Decoction on Cell Migration and Ocular Tumor Invasion inDrosophila

Xuefu Zhuyu Decoction (XFZYD), a Traditional Chinese Medicine (TCM) decoction mainly for treating blood stasis syndrome, has been widely investigated and applied in clinic and in laboratory. XFZYD contains 11 herbs and has been identified to promoting blood circulation to remove blood stasis for cardiovascular disease. Meanwhile, blood stasis is directly related to malignant tumor according to TCM basic theory. However, the effects of XFZYD on tumor metastasis and the underlying mechanisms are still largely unknown. Here, we employed well-establishedDrosophilacell migration and tumor invasion models to explore whether XFZYD has the anticancer activity on tumor metastasisin vivo. Our work has demonstrated that XFZYD could suppress cell migration and tumor invasion at the moderate concentrations. In addition, XFZYD altered the expression of MMP1,β-integrin, and E-cadherin to impede cell migration. Moreover, XFZYD inhibited ocular tumor invasion presumably by reducing the activity of Notch signaling. Together, these evidences reveal a positive role of XFZYD in suppressing cell migration and tumor metastasis, providing the potential drug targets and key clues for cancer clinical treatment strategies.

Using Drosophila Models and Tools to Understand the Mechanisms of Novel Human Cancer Driver Gene Function

The formation, overgrowth and metastasis of tumors comprise a complex series of cellular and molecular events resulting from the combined effects of a variety of aberrant signaling pathways, mutations, and epigenetic alterations. Modeling this complexity in vivo requires multiple genes to be manipulated simultaneously, which is technically challenging. Here, we analyze how Drosophila research can further contribute to identifying pathways and elucidating mechanisms underlying novel cancer driver (risk) genes associated with tumor growth and metastasis in humans.

Dynamic MAPK signaling activity underlies a transition from growth arrest to proliferation in Drosophila scribble mutant tumors

Human tumors exhibit plasticity and evolving capacity over time. It is difficult to study the mechanisms of how tumors change over time in human patients, in particular during the early stages when a few oncogenic cells are barely detectable. Here, we used a Drosophila tumor model caused by loss of scribble (scrib), a highly conserved apicobasal cell polarity gene, to investigate the spatial-temporal dynamics of early tumorigenesis events. The fly scrib mutant tumors have been successfully used to model many aspects of tumorigenesis processes. However, it is still unknown whether Drosophila scrib mutant tumors exhibit plasticity and evolvability along the temporal axis. We found that scrib mutant tumors displayed different growth rates and cell cycle profiles over time, indicative of a growth arrest-to-proliferation transition as the scrib mutant tumors progress. Longitudinal bulk and single-cell transcriptomic analysis of scrib mutant tumors revealed that the MAPK pathway, including JNK and ERK signaling activities, showed quantitative changes over time. We found that high JNK signaling activity caused G2/M cell cycle arrest in early scrib mutant tumors. In addition, JNK signaling activity displayed a radial polarity with the JNK^high cells located at the periphery of scrib mutant tumors, providing an inherent mechanism that leads to an overall decrease in JNK signaling activity over time. We also found that ERK signaling activity, in contrast to JNK activity, increased over time and promoted growth in late-stage scrib mutant tumors. Furthermore, high JNK signaling activity repressed ERK signaling activity in early scrib mutant tumors. Together, these data demonstrate that dynamic MAPK signaling activity, fueled by intratumor heterogeneity derived from tissue topological differences, drives a growth arrest-to-proliferation transition in scrib mutant tumors.

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

Summary: The authors provide evidence to show that a well-established Drosophila tumor model, caused by loss of apicobasal cell polarity, harbors a surprising degree of plasticity and evolvability along the temporal axis.

JNK-dependent cell cycle stalling in G2 promotes survival and senescence-like phenotypes in tissue stress

The restoration of homeostasis after tissue damage relies on proper spatial-temporal control of damage-induced apoptosis and compensatory proliferation. In Drosophila imaginal discs these processes are coordinated by the stress response pathway JNK. We demonstrate that JNK signaling induces a dose-dependent extension of G2 in tissue damage and tumors, resulting in either transient stalling or a prolonged but reversible cell cycle arrest. G2-stalling is mediated by downregulation of the G2/M-specific phosphatase String(Stg)/Cdc25. Ectopic expression of stg is sufficient to suppress G2-stalling and reveals roles for stalling in survival, proliferation and paracrine signaling. G2-stalling protects cells from JNK-induced apoptosis, but under chronic conditions, reduces proliferative potential of JNK-signaling cells while promoting non-autonomous proliferation. Thus, transient cell cycle stalling in G2 has key roles in wound healing but becomes detrimental upon chronic JNK overstimulation, with important implications for chronic wound healing pathologies or tumorigenic transformation.

Prp8 regulates oncogene-induced hyperplastic growth in Drosophila

Although developmental signalling pathways control tumourigenic growth, the cellular mechanisms that abnormally proliferating cells rely on are still largely unknown. Drosophila melanogaster is a genetically tractable model that is used to study how specific genetic changes confer advantageous tumourigenic traits. Despite recent efforts, the role of deubiquitylating enzymes in cancer is particularly understudied. We performed a Drosophila in vivo RNAi screen to identify deubiquitylating enzymes that modulate Ras^V12-induced hyperplastic growth. We identified the spliceosome core component Prp8 as a crucial regulator of Ras-, EGFR-, Notch- or RET-driven hyperplasia. Loss of prp8 function alone decreased cell proliferation, increased cell death, and affected cell differentiation and polarity. In hyperplasia, Prp8 supported tissue overgrowth independently of caspase-dependent cell death. The depletion of prp8 efficiently blocked Ras-, EGFR- and Notch-driven tumours but, in contrast, enhanced tumours that were driven by oncogenic RET, suggesting a context-specific role in hyperplasia. These data show, for the first time, that Prp8 regulates hyperplasia, and extend recent observations on the potential role of the spliceosome in cancer. Our findings suggest that targeting Prp8 could be beneficial in specific tumour types.

Summary: Prp8 has been identified as a modulator of oncogenic growth in multiple Drosophila cancer models, which suggests the spliceosome as a potential context-dependent target in cancers.

PP6 Disruption Synergizes with Oncogenic Ras to Promote JNK-Dependent Tumor Growth and Invasion

RAS genes are frequently mutated in cancers, yet an effective treatment has not been developed, partly because of an incomplete understanding of signaling within Ras-related tumors. To address this, we performed a genetic screen in Drosophila, aiming to find mutations that cooperate with oncogenic Ras (Ras^V12) to induce tumor overgrowth and invasion. We identified fiery mountain (fmt), a regulatory subunit of the protein phosphatase 6 (PP6) complex, as a tumor suppressor that synergizes with Ras^V12 to drive c-Jun N-terminal kinase (JNK)-dependent tumor growth and invasiveness. We show that Fmt negatively regulates JNK upstream of dTAK1. We further demonstrate that disruption of PpV, the catalytic subunit of PP6, mimics fmt loss-of-function-induced tumorigenesis. Finally, Fmt synergizes with PpV to inhibit JNK-dependent tumor progression. Our data here further highlight the power of Drosophila as a model system to unravel molecular mechanisms that may be relevant to human cancer biology.

Modelling Cooperative Tumorigenesis in Drosophila

The development of human metastatic cancer is a multistep process, involving the acquisition of several genetic mutations, tumour heterogeneity, and interactions with the surrounding microenvironment. Due to the complexity of cancer development in mammals, simpler model organisms, such as the vinegar fly, Drosophila melanogaster, are being utilized to provide novel insights into the molecular mechanisms involved. In this review, we highlight recent advances in modelling tumorigenesis using the Drosophila model, focusing on the cooperation of oncogenes or tumour suppressors, and the interaction of mutant cells with the surrounding tissue in epithelial tumour initiation and progression.

Epithelial tumors: Growing from within

The growth of epithelial tumors is often governed by cell interactions with the surrounding stroma. Drosophila has been instrumental in identifying the relevant molecular elements mediating these interactions. Of note is the role of the TNF ligand Eiger, released from recruited blood cells, in activating the JNK tumor-promoting pathway in epithelial tumors. JNK drives the transcriptional induction of mitogenic molecules, matrix metalloproteases and systemic signals that lead to tumor growth, tissue invasiveness and malignancy. Here we review our findings on a tumor-intrinsic, Eiger- and stroma-independent mechanism that contributes to the unlimited growth potential of tumors caused either by chromosomal instability or impaired cell polarity. This newly identified mechanism, which was revealed in an experimental condition in which contacts between tumor cells and wild-type epithelial cells were minimized, relies on interactions between functionally distinct tumor cell populations that activate JNK in a cell-autonomous manner. We discuss the impact of cell interaction-based feedback amplification loops on the unlimited growth potential of epithelial tumors. These findings are expected to contribute to the identification of the relevant cell populations and molecular mechanisms to be targeted in drug therapy.

POSH regulates Hippo signaling through ubiquitin-mediated expanded degradation

The Hippo signaling pathway is a master regulator of organ growth, tissue homeostasis, and tumorigenesis. The activity of the Hippo pathway is controlled by various upstream components, including Expanded (Ex), but the precise molecular mechanism of how Ex is regulated remains poorly understood. Here we identify Plenty of SH3s (POSH), an E3 ubiquitin ligase, as a key component of Hippo signaling in DrosophilaPOSH overexpression synergizes with loss of Kibra to induce overgrowth and up-regulation of Hippo pathway target genes. Furthermore, knockdown of POSH impedes dextran sulfate sodium-induced Yorkie-dependent intestinal stem cell renewal, suggesting a physiological role of POSH in modulating Hippo signaling. Mechanistically, POSH binds to the C-terminal of Ex and is essential for the Crumbs-induced ubiquitination and degradation of Ex. Our findings establish POSH as a crucial regulator that integrates the signal from the cell surface to negatively regulate Ex-mediated Hippo activation in Drosophila.

Feedback amplification loop drives malignant growth in epithelial tissues

Interactions between cells bearing oncogenic mutations and the surrounding microenvironment, and cooperation between clonally distinct cell populations, can contribute to the growth and malignancy of epithelial tumors. The genetic techniques available in Drosophila have contributed to identify important roles of the TNF-α ligand Eiger and mitogenic molecules in mediating these interactions during the early steps of tumor formation. Here we unravel the existence of a tumor-intrinsic-and microenvironment-independent-self-reinforcement mechanism that drives tumor initiation and growth in an Eiger-independent manner. This mechanism relies on cell interactions between two functionally distinct cell populations, and we present evidence that these cell populations are not necessarily genetically different. Tumor-specific and cell-autonomous activation of the tumorigenic JNK stress-activated pathway drives the expression of secreted signaling molecules and growth factors to delaminating cells, which nonautonomously promote proliferative growth of the partially transformed epithelial tissue. We present evidence that cross-feeding interactions between delaminating and nondelaminating cells increase each other's sizes and that these interactions can explain the unlimited growth potential of these tumors. Our results will open avenues toward our molecular understanding of those social cell interactions with a relevant function in tumor initiation in humans.

The Immune Phenotype of Three Drosophila Leukemia Models

Many leukemia patients suffer from dysregulation of their immune system, making them more susceptible to infections and leading to general weakening (cachexia). Both adaptive and innate immunity are affected. The fruit fly Drosophila melanogaster has an innate immune system, including cells of the myeloid lineage (hemocytes). To study Drosophila immunity and physiology during leukemia, we established three models by driving expression of a dominant-active version of the Ras oncogene (Ras^V12 ) alone or combined with knockdowns of tumor suppressors in Drosophila hemocytes. Our results show that phagocytosis, hemocyte migration to wound sites, wound sealing, and survival upon bacterial infection of leukemic lines are similar to wild type. We find that in all leukemic models the two major immune pathways (Toll and Imd) are dysregulated. Toll-dependent signaling is activated to comparable extents as after wounding wild-type larvae, leading to a proinflammatory status. In contrast, Imd signaling is suppressed. Finally, we notice that adult tissue formation is blocked and degradation of cell masses during metamorphosis of leukemic lines, which is akin to the state of cancer-dependent cachexia. To further analyze the immune competence of leukemic lines, we used a natural infection model that involves insect-pathogenic nematodes. We identified two leukemic lines that were sensitive to nematode infections. Further characterization demonstrates that despite the absence of behavioral abnormalities at the larval stage, leukemic larvae show reduced locomotion in the presence of nematodes. Taken together, this work establishes new Drosophila models to study the physiological, immunological, and behavioral consequences of various forms of leukemia.

Robo-Enabled Tumor Cell Extrusion

How aberrant cells are removed from a tissue to prevent tumor formation is a key question in cancer biology. Reporting in this issue of Developmental Cell, Vaughen and Igaki (2016) show that a pathway with an important role in neural guidance also directs extrusion of tumor cells from epithelial tissues.

Hippo signaling promotes JNK-dependent cell migration

Overwhelming studies show that dysregulation of the Hippo pathway is positively correlated with cell proliferation, growth, and tumorigenesis. Paradoxically, the detailed molecular roles of the Hippo pathway in cell invasion remain debatable. Using a Drosophila invasion model in wing epithelium, we show herein that activated Hippo signaling promotes cell invasion and epithelial-mesenchymal transition through JNK, as inhibition of JNK signaling dramatically blocked Hippo pathway activation-induced matrix metalloproteinase 1 expression and cell invasion. Furthermore, we identify bantam-Rox8 modules as essential components downstream of Yorkie in mediating JNK-dependent cell invasion. Finally, we confirm that YAP (Yes-associated protein) expression negatively regulates TIA1 (Rox8 ortholog) expression and cell invasion in human cancer cells. Together, these findings provide molecular insights into Hippo pathway-mediated cell invasion and also raise a noteworthy concern in therapeutic interventions of Hippo-related cancers, as simply inhibiting Yorkie or YAP activity might paradoxically accelerate cell invasion and metastasis.

Myc suppresses tumor invasion and cell migration by inhibiting JNK signaling

Tumor metastasis, but not primary overgrowth, is the leading cause of mortality for cancer patients. During the past decade, Drosophila melanogaster has been well-accepted as an excellent model to address the intrinsic mechanism of different aspects of cancer progression, ranging from tumor initiation to metastasis. In a genetic screen performed in Drosophila, aiming to find novel modulators of tumor invasion, we identified the oncoprotein Myc as a negative regulator. While expression of Myc dramatically blocks tumor invasion and cell migration, loss of Myc promotes cell migration in vivo. The activity of Myc is further enhanced by the co-expression of its transcription partner Max. Mechanistically, we found Myc/Max directly upregulates the transcription of puc, which encodes an inhibitor of JNK signaling crucial for tumor invasion and cell migration. Furthermore, we demonstrated that human cMyc potently suppresses JNK-dependent cell invasion and migration in both Drosophila and lung adenocarcinoma cell lines. These findings provide novel molecular insights into Myc-mediated cancer progression and raise the noteworthy problem in therapeutic strategies as inhibiting Myc might conversely accelerate tumor metastasis.

The SWI/SNF Complex Protein Snr1 Is a Tumor Suppressor in Drosophila Imaginal Tissues

Components of the SWI/SNF chromatin-remodeling complex are among the most frequently mutated genes in various human cancers, yet only SMARCB1/hSNF5, a core member of the SWI/SNF complex, is mutated in malignant rhabdoid tumors (MRT). How SMARCB1/hSNF5 functions differently from other members of the SWI/SNF complex remains unclear. Here, we use Drosophila imaginal epithelial tissues to demonstrate that Snr1, the conserved homolog of human SMARCB1/hSNF5, prevents tumorigenesis by maintaining normal endosomal trafficking-mediated signaling cascades. Removal of Snr1 resulted in neoplastic tumorigenic overgrowth in imaginal epithelial tissues, whereas depletion of any other members of the SWI/SNF complex did not induce similar phenotypes. Unlike other components of the SWI/SNF complex that were detected only in the nucleus, Snr1 was observed in both the nucleus and the cytoplasm. Aberrant regulation of multiple signaling pathways, including Notch, JNK, and JAK/STAT, was responsible for tumor progression upon snr1-depletion. Our results suggest that the cytoplasmic Snr1 may play a tumor suppressive role in Drosophila imaginal tissues, offering a foundation for understanding the pivotal role of SMARCB1/hSNF5 in suppressing MRT during early childhood. Cancer Res; 77(4); 862-73. ©2017 AACR.

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.

Cell Competition During Growth and Regeneration

Tissue growth and regeneration are autonomous, stem-cell-mediated processes in which stem cells within the organ self-renew and differentiate to create new cells, leading to new tissue. The processes of growth and regeneration require communication and interplay between neighboring cells. In particular, cell competition, which is a process in which viable cells are actively eliminated by more competitive cells, has been increasingly implicated to play an important role. Here, we discuss the existing literature regarding the current landscape of cell competition, including classical pathways and models, fitness fingerprint mechanisms, and immune system mechanisms of cell competition. We further discuss the clinical relevance of cell competition in the physiological processes of tissue growth and regeneration, highlighting studies in clinically important disease models, including oncological, neurological, and cardiovascular diseases.

Gene Dosage Imbalance Contributes to Chromosomal Instability-Induced Tumorigenesis

Chromosomal instability (CIN) is thought to be a source of mutability in cancer. However, CIN often results in aneuploidy, which compromises cell fitness. Here, we used the dosage compensation mechanism (DCM) of Drosophila to demonstrate that chromosome-wide gene dosage imbalance contributes to the deleterious effects of CIN-induced aneuploidy and its pro-tumorigenic action. We present evidence that resetting of the DCM counterbalances the damaging effects caused by CIN-induced changes in X chromosome number. Importantly, interfering with the DCM suffices to mimic the cellular effects of aneuploidy in terms of reactive oxygen species (ROS) production, JNK-dependent cell death, and tumorigenesis upon apoptosis inhibition. We unveil a role of ROS in JNK activation and a variety of cellular and tissue-wide mechanisms that buffer the deleterious effects of CIN, including DNA-damage repair, activation of the p38 pathway, and cytokine induction to promote compensatory proliferation. Our data reveal the existence of robust compensatory mechanisms that counteract CIN-induced cell death and tumorigenesis.

Stem-Cell-Based Tumorigenesis in Adult Drosophila

Recent studies suggest that a small subset of cells within a tumor, the so-called cancer stem cells (CSCs), are responsible for tumor propagation, relapse, and the eventual death of most cancer patients. CSCs may derive from a few tumor-initiating cells, which are either transformed normal stem cells or reprogrammed differentiated cells after acquiring initial cancer-causing mutations. CSCs and normal stem cells share some properties, but CSCs differ from normal stem cells in their tumorigenic ability. Notably, CSCs are usually resistant to chemo- and radiation therapies. Despite the apparent roles of CSCs in human cancers, the biology underlying their behaviors remains poorly understood. Over the past few years, studies in Drosophila have significantly contributed to this new frontier of cancer research. Here, we first review how stem-cell tumors are initiated and propagated in Drosophila, through niche appropriation in the posterior midgut and through stem-cell competition for niche occupancy in the testis. We then discuss the differences between normal and tumorigenic stem cells, revealed by studying Ras^V12-transformed stem-cell tumors in the Drosophila kidney. Finally, we review the biology behind therapy resistance, which has been elucidated through studies of stem-cell resistance and sensitivity to death inducers using female germline stem cells and intestinal stem cells of the posterior midgut. We expect that screens using adult Drosophila neoplastic stem-cell tumor models will be valuable for identifying novel and effective compounds for treating human cancers.

Eiger-induced cell death relies on Rac1-dependent endocytosis

Signaling via tumor necrosis factor receptor (TNFR) superfamily members regulates cellular life and death decisions. A subset of mammalian TNFR proteins, most notably the p75 neurotrophin receptor (p75NTR), induces cell death through a pathway that requires activation of c-Jun N-terminal kinases (JNKs). However the receptor-proximal signaling events that mediate this remain unclear. Drosophila express a single tumor necrosis factor (TNF) ligand termed Eiger (Egr) that activates JNK-dependent cell death. We have exploited this model to identify phylogenetically conserved signaling events that allow Egr to induce JNK activation and cell death in vivo. Here we report that Rac1, a small GTPase, is specifically required in Egr-mediated cell death. rac1 loss of function blocks Egr-induced cell death, whereas Rac1 overexpression enhances Egr-induced killing. We identify Vav as a GEF for Rac1 in this pathway and demonstrate that dLRRK functions as a negative regulator of Rac1 that normally acts to constrain Egr-induced death. Thus dLRRK loss of function increases Egr-induced cell death in the fly. We further show that Rac1-dependent entry of Egr into early endosomes is a crucial prerequisite for JNK activation and for cell death and show that this entry requires the activity of Rab21 and Rab7. These findings reveal novel regulatory mechanisms that allow Rac1 to contribute to Egr-induced JNK activation and cell death.

Somatic mosaicism: on the road to cancer

Diversity is the basis of fitness selection. Although the genome of an individual is considered to be largely stable, there is theoretical and experimental evidence--both in model organisms and in humans--that genetic mosaicism is the rule rather than the exception. The continuous generation of cell variants, their interactions and selective pressures lead to life-long tissue dynamics. Individuals may thus enjoy 'clonal health', defined as a clonal composition that supports healthy morphology and physiology, or suffer from clonal configurations that promote disease, such as cancer. The contribution of mosaicism to these processes starts during embryonic development. In this Opinion article, we argue that the road to cancer might begin during these early stages.

JAK/STAT signalling mediates cell survival in response to tissue stress

Tissue homeostasis relies on the ability of tissues to respond to stress. Tissue regeneration and tumour models in Drosophila have shown that JNK is a prominent stress-response pathway promoting injury-induced apoptosis and compensatory proliferation. A central question remaining unanswered is how both responses are balanced by activation of a single pathway. JAK/STAT signalling, a potential JNK target, is implicated in promoting compensatory proliferation. While we observe JAK/STAT activation in imaginal discs upon damage, our data demonstrates that JAK/STAT and its downstream effector Zfh2 promote survival of JNK-signalling cells instead. The JNK component fos and the pro-apoptotic gene hid are regulated in a JAK/STAT-dependent manner. This molecular pathway restrains JNK-induced apoptosis and spatial propagation of JNK-signalling, thereby limiting the extent of tissue damage, as well as facilitating systemic and proliferative responses to injury. We find that the pro-survival function of JAK/STAT also drives tumour growth under conditions of chronic stress. Our study defines JAK/STAT function in tissue stress and illustrates how crosstalk between conserved signalling pathways establishes an intricate equilibrium between proliferation, apoptosis and survival to restore tissue homeostasis.

The Drosophila Chitinase-Like Protein IDGF3 Is Involved in Protection against Nematodes and in Wound Healing

Chitinase-like proteins (CLPs) of the 18 glycosyl hydrolase family retain structural similarity to chitinases but lack enzymatic activity. Although CLPs are upregulated in several human disorders that affect regenerative and inflammatory processes, very little is known about their normal physiological function. We show that an insect CLP (Drosophila imaginal disc growth factor 3, IDGF3) plays an immune-protective role during entomopathogenic nematode (EPN) infections. During these infections, nematodes force their entry into the host via border tissues, thus creating wounds. Whole-genome transcriptional analysis of nematode-infected wild-type and Idgf3 mutant larvae have shown that, in addition to the regulation of genes related to immunity and wound closure, IDGF3 represses Jak/STAT and Wingless signaling. Further experiments have confirmed that IDGF3 has multiple roles in innate immunity. It serves as an essential component required for the formation of hemolymph clots that seal wounds, and Idgf3 mutants display an extended developmental delay during wound healing. Altogether, our findings indicate that vertebrate and invertebrate CLP proteins function in analogous settings and have a broad impact on inflammatory reactions and infections. This opens the way to further genetic analysis of Drosophila IDGF3 and will help to elucidate the exact molecular context of CLP function.

Dally Proteoglycan Mediates the Autonomous and Nonautonomous Effects on Tissue Growth Caused by Activation of the PI3K and TOR Pathways

How cells acquiring mutations in tumor suppressor genes outcompete neighboring wild-type cells is poorly understood. The phosphatidylinositol 3-kinase (PI3K)–phosphatase with tensin homology (PTEN) and tuberous sclerosis complex (TSC)-target of rapamycin (TOR) pathways are frequently activated in human cancer, and this activation is often causative of tumorigenesis. We utilized the Gal4-UAS system in Drosophila imaginal primordia, highly proliferative and growing tissues, to analyze the impact of restricted activation of these pathways on neighboring wild-type cell populations. Activation of these pathways leads to an autonomous induction of tissue overgrowth and to a remarkable nonautonomous reduction in growth and proliferation rates of adjacent cell populations. This nonautonomous response occurs independently of where these pathways are activated, is functional all throughout development, takes place across compartments, and is distinct from cell competition. The observed autonomous and nonautonomous effects on tissue growth rely on the up-regulation of the proteoglycan Dally, a major element involved in modulating the spreading, stability, and activity of the growth promoting Decapentaplegic (Dpp)/transforming growth factor β(TGF-β) signaling molecule. Our findings indicate that a reduction in the amount of available growth factors contributes to the outcompetition of wild-type cells by overgrowing cell populations. During normal development, the PI3K/PTEN and TSC/TOR pathways play a major role in sensing nutrient availability and modulating the final size of any developing organ. We present evidence that Dally also contributes to integrating nutrient sensing and organ scaling, the fitting of pattern to size.

The loss of tumor suppressor genes induces a nonautonomous reduction of growth and proliferation rates in adjacent cell populations by competing for available growth factors; the proteoglycan Dally helps to mediate this effect.

The final size of a developing organ is finely modulated by nutrient conditions through the activity of nutrient sensing pathways, and deregulation of these pathways is often causative of tumorigenesis. Besides the well-known roles of these pathways in inducing tissue and cell growth, here we identify a nonautonomous effect of activation of these pathways on growth and proliferation rates and on the final size of neighboring cell populations. We reveal that the observed autonomous and nonautonomous effects on tissue growth and proliferation rates rely on the up-regulation of the proteoglycan Dally, a major factor involved in modulating the spreading, stability, and activity of the growth promoting Decapentaplegic (Dpp)/transforming growth factor β(TGF-β) signaling molecule. Our data indicate that a reduction in the amount of available growth factors contributes to the outcompetition of wild-type cells by overgrowing cell populations. Whereas nutrient-sensing pathways modulate the final size of the adult structure according to nutrient availability to the feeding animal, Dpp plays an organ-intrinsic role in the coordination of growth and patterning. We identify the proteoglycan Dally as the rate-limiting factor that contributes to the tissue-autonomous and nonautonomous effects on growth caused by targeted activation of the nutrient-sensing pathways. Thus, our results unravel a role of Dally as a molecular bridge between the organ-intrinsic and organ-extrinsic mechanisms that regulate organ size.

A Flippase-Mediated GAL80/GAL4 Intersectional Resource for Dissecting Appendage Development in Drosophila

Drosophila imaginal discs provide an ideal model to study processes important for cell signaling and cell specification, tissue differentiation, and cell competition during development. One challenge to understanding genetic control of cellular processes and cell interactions is the difficulty in effectively targeting a defined subset of cells in developing tissues in gene manipulation experiments. A recently developed Flippase-induced intersectional GAL80/GAL4 repression method incorporates several gene manipulation technologies in Drosophila to enable such fine-scale dissection in neural tissues. In particular, this approach brings together existing GAL4 transgenes, newly developed enhancer-trap flippase transgenes, and GAL80 transgenes flanked by Flippase recognition target sites. The combination of these tools enables gene activation/repression in particular subsets of cells within a GAL4 expression pattern. Here, we expand the utility of a large collection of these enhancer-trap flippase transgenic insertion lines by characterizing their expression patterns in third larval instar imaginal discs. We screened 521 different enhancer-trap flippase lines and identified 28 that are expressed in imaginal tissues, including two transgenes that show sex-specific expression patterns. Using a line that expresses Flippase in the wing imaginal disc, we demonstrate the utility of this intersectional approach for studying development by knocking down gene expression of a key member of the planar cell polarity pathway. The results of our experiments show that these enhancer-trap flippase lines enable fine-scale manipulation in imaginal discs.

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.

Sterile inflammation in Drosophila

The study of immune responses in Drosophila has already yielded significant results with impacts on our understanding of vertebrate immunity, such as the characterization of the Toll receptor. Several recent papers have focused on the humoral response to damage signals rather than pathogens, particularly damage signals from tumour-like tissues generated by loss of cell polarity or chromosomal instability. Both the triggers that generate this sterile inflammation and the systemic and local effects of it are only just beginning to be characterized in Drosophila. Here we review the molecular mechanisms that are known that give rise to the recruitment of Drosophila phagocytes, called hemocytes, as well as the signals, such as TNFα, that stimulated hemocytes emit at sites of perceived damage. The signalling consequences of inflammation, such as the activation of JNK, and the potential for modifying this response are also discussed.

Cell membrane fluid-mosaic structure and cancer metastasis

Cancer cells are surrounded by a fluid-mosaic membrane that provides a highly dynamic structural barrier with the microenvironment, communication filter and transport, receptor and enzyme platform. This structure forms because of the physical properties of its constituents, which can move laterally and selectively within the membrane plane and associate with similar or different constituents, forming specific, functional domains. Over the years, data have accumulated on the amounts, structures, and mobilities of membrane constituents after transformation and during progression and metastasis. More recent information has shown the importance of specialized membrane domains, such as lipid rafts, protein-lipid complexes, receptor complexes, invadopodia, and other cellular structures in the malignant process. In describing the macrostructure and dynamics of plasma membranes, membrane-associated cytoskeletal structures and extracellular matrix are also important, constraining the motion of membrane components and acting as traction points for cell motility. These associations may be altered in malignant cells, and probably also in surrounding normal cells, promoting invasion and metastatic colonization. In addition, components can be released from cells as secretory molecules, enzymes, receptors, large macromolecular complexes, membrane vesicles, and exosomes that can modify the microenvironment, provide specific cross-talk, and facilitate invasion, survival, and growth of malignant cells.

A drosophila genetic resource of mutants to study mechanisms underlying human genetic diseases

Invertebrate model systems are powerful tools for studying human disease owing to their genetic tractability and ease of screening. We conducted a mosaic genetic screen of lethal mutations on the Drosophila X chromosome to identify genes required for the development, function, and maintenance of the nervous system. We identified 165 genes, most of whose function has not been studied in vivo. In parallel, we investigated rare variant alleles in 1,929 human exomes from families with unsolved Mendelian disease. Genes that are essential in flies and have multiple human homologs were found to be likely to be associated with human diseases. Merging the human data sets with the fly genes allowed us to identify disease-associated mutations in six families and to provide insights into microcephaly associated with brain dysgenesis. This bidirectional synergism between fly genetics and human genomics facilitates the functional annotation of evolutionarily conserved genes involved in human health.

Loss of Rab5 drives non-autonomous cell proliferation through TNF and Ras signaling in Drosophila

Deregulation of the endocytic machinery has been implicated in human cancers. However, the mechanism by which endocytic defects drive cancer development remains to be clarified. Here, we find through a genetic screen in Drosophila that loss of Rab5, a protein required for early endocytic trafficking, drives non-autonomous cell proliferation in imaginal epithelium. Our genetic data indicate that dysfunction of Rab5 leads to cell-autonomous accumulation of Eiger (a TNF homolog) and EGF receptor (EGFR), which causes activation of downstream JNK and Ras signaling, respectively. JNK signaling and its downstream component Cdc42 cooperate with Ras signaling to induce upregulation of a secreted growth factor Upd (an IL-6 homolog) through inactivation of the Hippo pathway. Such non-autonomous tissue growth triggered by Rab5 defect could contribute to epithelial homeostasis as well as cancer development within heterogeneous tumor microenvironment.

Dissecting tumour heterogeneity in flies: genetic basis of interclonal oncogenic cooperation

Cancers develop through sequential acquisition of oncogenic mutations, indicating a crucial role of genetic alterations in tumour progression. However, accumulating evidence suggests that cancers also progress towards malignancy through cell-cell interactions within heterogeneous tumour tissue. Recent studies have indicated that tumour heterogeneity not only contributes to drug resistance and tumour recurrence but also plays an active role in promoting tumour progression. Especially, genetic studies in Drosophila have discovered novel types of tumour progression through cell-cell interactions and have dissected the underlying mechanisms. This review focuses on describing recent findings obtained from Drosophila genetics that provide genetic basis of interclonal oncogenic cooperation in heterogeneous tumour tissue.

Tissue design: how Drosophila tumors remodel their neighborhood

Drosophila genetics has long been appreciated as a powerful approach for discovering the normal functions of genes that act as oncogenes and tumor suppressors in human cancer. Recent studies have also highlighted its advantages for deciphering how such genes function during tumorigenesis itself. Here we detail studies relating to how tumors, generated in developing organs and adult stem cell-based tissues, remodel the tissue landscape to their benefit. Like mammalian tumors, insect tumors can dissolve extracellular matrix, recruit blood cells, migrate and invade other tissues. While much is known about how mammalian fibroblasts, immune cells and vasculature promote late tumorigenesis, less is understood about the very earliest stages of tumor development in mammals. Because Drosophila has fewer mitotic cells and a simpler tissue architecture, it affords easy detection and analysis of early clonal tumor growth. Drosophila studies have revealed both cooperative and competitive interactions between tumor and normal cells during early tumor growth. During development, these interactions typically occur with other proliferative progenitor cells, but in adult stem cell-based tissues, the stem cell niche can fuel tumor growth.