Loss of cell polarity drives tumor growth and invasion through JNK activation in Drosophila

Epithelial cell-fate switch triggering ectopic ligand-receptor-mediated JAK-STAT signaling promotes tumorigenesis in Drosophila

Disruption of epithelial architecture is a hallmark of human malignant cancers, yet whether and how epithelial deformation influences tumor progression has been elusive. Here, through a genetic screen in Drosophila eye disc, we explored mutations that potently promoted Ras-activated (RasV12) tumor growth and identified eyes absent (eya), an eye determination gene, whose mutation compromised tissue growth but synergized with RasV12 to cause massive overgrowth. Furthermore, induction of cell-fate switch by mis-expression of Abd-B in the eye disc also induced massive RasV12 overgrowth. Mechanistically, cell-fate switch caused epithelial invagination accompanied by partial mislocalization of the transmembrane receptor Domeless (Dome) from the apical to the basal membrane of the eye epithelium, where its ligand Unpaired3 (Upd3) is present. This led to JAK-STAT activation that cooperates with RasV12 to drive tumor progression. Our data provide a mechanistic explanation for how cell-fate switch and subsequent epithelial deformation creates a cancer-prone environment in the epithelium.

The mechanical state of pre-tumoral epithelia controls subsequent Drosophila tumor aggressiveness

Tumors evolve through the acquisition of increasingly aggressive traits associated with dysplasia. This progression is accompanied by alterations in tumor mechanical properties, especially through extracellular matrix remodeling. However, the contribution of pre-tumoral tissue mechanics to tumor aggressiveness remains poorly known in vivo. Here, we show that adherens junction tension in pre-tumoral tissues dictates subsequent tumor evolution in Drosophila. Increased cell contractility, observed in aggressive tumors before any sign of tissue overgrowth, proved sufficient to trigger dysplasia in normally hyperplastic tumors. In addition, high contractility precedes any changes in cell polarity and contributes to tumor evolution through cell death induction, which favors cell-cell junction weakening. Overall, our results highlight the need to re-evaluate the roles of tumoral cell death and identify pre-tumoral cell mechanics as an unsuspected early marker and key trigger of tumor aggressiveness.

Activation of the Drosophila innate immune system accelerates growth in cooperation with oncogenic Ras

Innate immunity in Drosophila acts as an organismal surveillance system for external stimuli or cellular fitness and triggers context-specific responses to fight infections and maintain tissue homeostasis. However, uncontrolled activation of innate immune pathways can be detrimental. In mammals, innate immune signaling is often overactivated in malignant cells and contributes to tumor progression. Drosophila tumor models have been instrumental in the discovery of interactions between pathways that promote tumorigenesis, but little is known about whether and how the Toll innate immune pathway interacts with oncogenes. Here we use a Drosophila epithelial in vivo model to investigate the interplay between Toll signaling and oncogenic Ras. In the absence of oncogenic Ras (RasV12), Toll signaling suppresses differentiation and induces apoptosis. In contrast, in the context of RasV12, cells are protected from cell death and Dorsal promotes cell survival and proliferation to drive hyperplasia. Taken together, we show that the tissue-protective functions of innate immune activity can be hijacked by pre-malignant cells to induce tumorous overgrowth.

Functions of Drosophila Toll/NF-κB signaling in imaginal tissue homeostasis and cancer

The Toll/NF-κB pathway plays a central role in patterning the Drosophila embryo and in orchestrating the innate immune response against microbial infections. Both discoveries were associated with a Nobel Prize award and led to the recognition of the Toll-like receptor pathway in mammals, which has significant implications for diseases. Recent discoveries have revealed that the Toll/NF-κB pathway also maintains epithelial homeostasis of imaginal tissues during development: local Toll/NF-κB signaling activity monitors internal cellular fitness, and precancerous mutant cells can trigger systemic Toll/NF-κB pathway activation. However, this signaling can be exploited in diseases like cancer, in which Toll/NF-κB signaling is often co-opted or subverted. Various models have been proposed to explain how Toll/NF-κB signaling contributes to different types of cancer. Here we provide an overview of the functions of Toll/NF-κB signaling in imaginal tissue homeostasis with a focus on their misuse in pathological contexts, particularly their significance for tumor formation.

Epithelial Polarity Loss and Multilayer Formation: Insights Into Tumor Growth and Regulatory Mechanisms

Epithelial tissues serve as critical barriers in metazoan organisms, maintaining structural integrity and facilitating essential physiological functions. Epithelial cell polarity regulates mechanical properties, signaling, and transport, ensuring tissue organization and homeostasis. However, the barrier function is challenged by cell turnover during development and maintenance. To preserve tissue integrity while removing dying or unwanted cells, epithelial tissues employ cell extrusion. This process removes both dead and live cells from the epithelial layer, typically causing detached cells to undergo apoptosis. Transformed cells, however, often resist apoptosis, leading to multilayered structures and early carcinogenesis. Malignant cells may invade neighboring tissues. Loss of cell polarity can lead to multilayer formation, cell extrusion, and invasion. Recent studies indicate that multilayer formation in epithelial cells with polarity loss involves a mixture of wild-type and mutant cells, leading to apical or basal accumulation. The directionality of accumulation is regulated by mutations in polarity complex genes. This phenomenon, distinct from traditional apical or basal extrusion, exhibits similarities to the endophytic or exophytic growth observed in human tumors. This review explores the regulation and implications of these phenomena for tissue biology and disease pathology.

JNK Kinase regulates cachexia like syndrome in scribble knockdown tumor model of Drosophila melanogaster

Cachexia and systemic organ wasting are metabolic syndrome often associated with cancer. However, the exact mechanism of cancer associated cachexia like syndrome still remain elusive. In this study, we utilized a scribble (scrib) knockdown induced hindgut tumor to investigate the role of JNK kinase in cachexia like syndrome. Scrib, a cell polarity regulator, also acts as a tumor suppressor gene. Its loss and mis-localization are reported in various type of malignant cancer-like breast, colon and prostate cancer. The scrib knockdown flies exhibited male lethality, reduced life span, systemic organ wasting and increased pJNK level in hindgut of female flies. Interestingly, knocking down of human JNK Kinase analogue, hep, in scrib knockdown background in hindgut leads to restoration of loss of scrib mediated lethality and systemic organ wasting. Our data showed that scrib loss in hindgut is capable of inducing cancer associated cachexia like syndrome. Here, we firstly report that blocking the JNK signaling pathway effectively rescued the cancer cachexia induced by scrib knockdown, along with its associated gut barrier disruption. These findings have significantly advanced our understanding of cancer cachexia and have potential implications for the development of therapeutic strategies. However, more research is needed to fully understand the complex mechanisms underlying this condition.

Flamingo participates in multiple models of cell competition

The growth and survival of cells with different fitness, such as those with a proliferative advantage or a deleterious mutation, is controlled through cell competition. During development, cell competition enables healthy cells to eliminate less fit cells that could jeopardize tissue integrity, and facilitates the elimination of pre-malignant cells by healthy cells as a surveillance mechanism to prevent oncogenesis. Malignant cells also benefit from cell competition to promote their expansion. Despite its ubiquitous presence, the mechanisms governing cell competition, particularly those common to developmental competition and tumorigenesis, are poorly understood. Here, we show that in Drosophila, the planar cell polarity (PCP) protein Flamingo (Fmi) is required by winners to maintain their status during cell competition in malignant tumors to overtake healthy tissue, in early pre-malignant cells when they overproliferate among wildtype cells, in healthy cells when they later eliminate pre-malignant cells, and by supercompetitors as they compete to occupy excessive territory within wildtype tissues. 'Would-be' winners that lack Fmi are unable to overproliferate, and instead become losers. We demonstrate that the role of Fmi in cell competition is independent of PCP, and that it uses a distinct mechanism that may more closely resemble one used in other less well-defined functions of Fmi.

Autocrine glutamate signaling drives cell competition in Drosophila

Cell competition is an evolutionarily conserved quality control process that eliminates suboptimal or potentially dangerous cells. Although differential metabolic states act as direct drivers of competition, how these are measured across tissues is not understood. Here, we demonstrate that vesicular glutamate transporter (VGlut) and autocrine glutamate signaling are required for cell competition and Myc-driven super-competition in the Drosophila epithelia. We find that the loss of glutamate-stimulated VGlut>NMDAR>CaMKII>CrebB signaling triggers loser status and cell death under competitive settings via the autocrine induction of TNF. This in turn drives TNFR>JNK activation, triggering loser cell elimination and PDK/LDH-dependent metabolic reprogramming. Inhibiting caspases or preventing loser cells from transferring lactate to their neighbors nullifies cell competition. Further, in a Drosophila model for premalignancy, Myc-overexpressing clones co-opt this signaling circuit to acquire super-competitor status. Targeting glutamate signaling converts Myc "super-competitor" clones into "losers," highlighting new therapeutic opportunities to restrict the evolution of fitter clones.

An expanded view of cell competition

Cell competition arises in heterogeneous tissues when neighbouring cells sense their relative fitness and undergo selection. It has been a challenge to define contexts in which cell competition is a physiologically relevant phenomenon and to understand the cellular features that underlie fitness and fitness sensing. Drawing on examples across a range of contexts and length scales, we illuminate molecular and cellular features that could underlie fitness in diverse tissue types and processes to promote and reinforce long-term maintenance of tissue function. We propose that by broadening the scope of how fitness is defined and the circumstances in which cell competition can occur, the field can unlock the potential of cell competition as a lens through which heterogeneity and its role in the fundamental principles of complex tissue organisation can be understood.

Blockade of Crk eliminates Yki/YAP-activated tumors via JNK-mediated apoptosis in Drosophila

Selective elimination of cancer cells without causing deleterious effects on normal cells is an ideal anti-cancer strategy. Here, using Drosophila cancer model, we performed an in vivo RNAi screen for anti-cancer targets that selectively eliminate tumors without affecting normal tissue growth. In Drosophila imaginal epithelium, clones of cells expressing oncogenic Ras with simultaneous mutations in the cell polarity gene scribble (RasV12/scrib-/-) develop into malignant tumors. We found that knockdown of Crk, the Drosophila ortholog of human CRK (CT10 regulatory kinase) and CRKL (Crk-like) adapter proteins, significantly suppresses growth of RasV12/scrib-/- tumors by inducing c-Jun N-terminal kinase (JNK)-mediated apoptosis, while it does not affect growth of normal epithelium. Mechanistically, Crk inhibition blocks Yorkie (Yki)/YAP activity by impairing F-actin accumulation, an upstream event of Yki/YAP activation in tumors. Inhibition of Yki/YAP in tumors causes intracellular JNK signaling to be used for apoptosis induction. Given that molecules and signaling pathways identified in Drosophila are highly conserved and activated in human cancers, our findings would provide a novel, to the best of our knowledge, anti-cancer strategy against YAP-activated cancers.

The Drosophila tumor necrosis factor Eiger promotes Myc supercompetition independent of canonical Jun N-terminal kinase signaling

Numerous factors have been implicated in the cell-cell interactions that lead to elimination of cells via cell competition, a context-dependent process of cell selection in somatic tissues that is based on comparisons of cellular fitness. Here, we use a series of genetic tests in Drosophila to explore the relative contribution of the pleiotropic cytokine tumor necrosis factor α (TNFα) in Myc-mediated cell competition (also known as Myc supercompetition or Myc cell competition). We find that the sole Drosophila TNF, Eiger (Egr), its receptor Grindelwald (Grnd/TNF receptor), and the adaptor proteins Traf4 and Traf6 are required to eliminate wild-type "loser" cells during Myc cell competition. Although typically the interaction between Egr and Grnd leads to cell death by activating the intracellular Jun N-terminal kinase (JNK) stress signaling pathway, our experiments reveal that many components of canonical JNK signaling are dispensable for cell death in Myc cell competition, including the JNKKK Tak1, the JNKK Hemipterous and the JNK Basket. Our results suggest that Egr/Grnd signaling participates in Myc cell competition but functions in a role that is largely independent of the JNK signaling pathway.

Gp93 inhibits unfolded protein response-mediated c-Jun N-terminal kinase activation and cell invasion

In eukaryotes, Hsp90B1 serves as a vital chaperonin, facilitating the accurate folding of proteins. Interestingly, Hsp90B1 exhibits contrasting roles in the development of various types of cancers, although the underlying reasons for this duality remain enigmatic. Through the utilization of the Drosophila model, this study unveils the functional significance of Gp93, the Drosophila ortholog of Hsp90B1, which hitherto had limited reported developmental functions. Employing the Drosophila cell invasion model, we elucidated the pivotal role of Gp93 in regulating cell invasion and modulating c-Jun N-terminal kinase (JNK) activation. Furthermore, our investigation highlights the involvement of the unfolded protein response-associated IRE1/XBP1 pathway in governing Gp93 depletion-induced, JNK-dependent cell invasion. Collectively, these findings not only uncover a novel molecular function of Gp93 in Drosophila, but also underscore a significant consideration pertaining to the testing of Hsp90B1 inhibitors in cancer therapy.

A Tumor-Specific Molecular Network Promotes Tumor Growth in Drosophila by Enforcing a Jun N-Terminal Kinase-Yorkie Feedforward Loop

Cancer cells expand rapidly in response to altered intercellular and signaling interactions to achieve the hallmarks of cancer. Impaired cell polarity combined with activated oncogenes is known to promote several hallmarks of cancer, e.g., activating invasion by increased activity of Jun N-terminal kinase (JNK) and sustained proliferative signaling by increased activity of Hippo effector Yorkie (Yki). Thus, JNK, Yki, and their downstream transcription factors have emerged as synergistic drivers of tumor growth through pro-tumor signaling and intercellular interactions like cell competition. However, little is known about the signals that converge onto JNK and Yki in tumor cells and enable tumor cells to achieve the hallmarks of cancer. Here, using mosaic models of cooperative oncogenesis (RasV12,scrib-) in Drosophila, we show that RasV12,scrib- tumor cells grow through the activation of a previously unidentified network comprising Wingless (Wg), Dronc, JNK, and Yki. We show that RasV12,scrib- cells show increased Wg, Dronc, JNK, and Yki signaling, and all these signals are required for the growth of RasV12,scrib- tumors. We report that Wg and Dronc converge onto a JNK-Yki self-reinforcing positive feedback signal-amplification loop that promotes tumor growth. We found that the Wg-Dronc-Yki-JNK molecular network is specifically activated in polarity-impaired tumor cells and not in normal cells, in which apical-basal polarity remains intact. Our findings suggest that the identification of molecular networks may provide significant insights into the key biologically meaningful changes in signaling pathways and paradoxical signals that promote tumorigenesis.

Using Drosophila to uncover the role of organismal physiology and the tumor microenvironment in cancer

Cancer metastasis causes over 90% of cancer patient fatalities. Poor prognosis is determined by tumor type, the tumor microenvironment (TME), organ-specific biology, and animal physiology. While model organisms do not fully mimic the complexity of humans, many processes can be studied efficiently owing to the ease of genetic, developmental, and cell biology studies. For decades, Drosophila has been instrumental in identifying basic mechanisms controlling tumor growth and metastasis. The ability to generate clonal populations of distinct genotypes in otherwise wild-type animals makes Drosophila a powerful system to study tumor-host interactions at the local and global scales. This review discusses advancements in tumor biology, highlighting the strength of Drosophila for modeling TMEs and systemic responses in driving tumor progression and metastasis.

Cell competition: emerging signaling and unsolved questions

Multicellular communities have an intrinsic mechanism that optimizes their structure and function via cell-cell communication. One of the driving forces for such self-organization of the multicellular system is cell competition, the elimination of viable unfit or deleterious cells via cell-cell interaction. Studies in Drosophila and mammals have identified multiple mechanisms of cell competition caused by different types of mutations or cellular changes. Intriguingly, recent studies have found that different types of "losers" of cell competition commonly show reduced protein synthesis. In Drosophila, the reduction in protein synthesis levels in loser cells is caused by phosphorylation of the translation initiation factor eIF2α via a bZip transcription factor Xrp1. Given that a variety of cellular stresses converge on eIF2α phosphorylation and thus global inhibition of protein synthesis, cell competition may be a machinery that optimizes multicellular fitness by removing stressed cells. In this review, we summarize and discuss emerging signaling mechanisms and critical unsolved questions, as well as the role of protein synthesis in cell competition.

Cell competition and cancer from Drosophila to mammals

Throughout an individual's life, somatic cells acquire cancer-associated mutations. A fraction of these mutations trigger tumour formation, a phenomenon partly driven by the interplay of mutant and wild-type cell clones competing for dominance; conversely, other mutations function against tumour initiation. This mechanism of 'cell competition', can shift clone dynamics by evaluating the relative status of clonal populations, promoting 'winners' and eliminating 'losers'. This review examines the role of cell competition in the context of tumorigenesis, tumour progression and therapeutic intervention.

A Tumour-Specific Molecular Network Promotes Tumour Growth in Drosophila by Enforcing a JNK-YKI Feedforward Loop

Cancer cells expand rapidly in response to altered intercellular and signalling interactions to achieve hallmarks of cancer. Impaired cell polarity combined with activated oncogenes is known to promote several hallmarks of cancer e.g., activating invasion by increased activity of Jun N-terminal kinase (JNK), and sustained proliferative signalling by increased activity of Hippo effector Yorkie (Yki). Thus, JNK, Yki, and their downstream transcription factors have emerged as synergistic drivers of tumour growth through pro-tumour signalling and intercellular interactions like cell-competition. However, little is known about the signals that converge onto JNK and Yki in tumour cells that enable the tumour cells to achieve hallmarks of cancer. Here, using mosaic models of cooperative oncogenesis ( Ras V12 , scrib - ) in Drosophila , we show that Ras V12 , scrib - tumour cells grow by activation of a previously unidentified network comprising Wingless (Wg), Dronc, JNK and Yki. We show that Ras V12 , scrib - cells show increased Wg, Dronc, JNK, and Yki signalling, and all of these signals are required for the growth of Ras V12 , scrib - tumours. We report that Wg and Dronc converge onto a JNK-Yki self-reinforcing positive feedback signal-amplification loop that promotes tumour growth. We found that Wg-Dronc-Yki-JNK molecular network is specifically activated in polarity-impaired tumour cells and not in normal cells where apical basal polarity is intact. Our findings suggest that identification of molecular networks may provide significant insights about the key biologically meaningful changes in signalling pathways, and paradoxical signals that promote Tumourigenesis.

Slik maintains tissue homeostasis by preventing JNK-mediated apoptosis

BACKGROUND

The c-Jun N-terminal kinase (JNK) pathway is an evolutionarily conserved regulator of cell death, which is essential for coordinating tissue homeostasis. In this study, we have characterized the Drosophila Ste20-like kinase Slik as a novel modulator of JNK pathway-mediated apoptotic cell death.

RESULTS

First, ectopic JNK signaling-triggered cell death is enhanced by slik depletion whereas suppressed by Slik overexpression. Second, loss of slik activates JNK signaling, which results in enhanced apoptosis and impaired tissue homeostasis. In addition, genetic epistasis analysis suggests that Slik acts upstream of or in parallel to Hep to regulate JNK-mediated apoptotic cell death. Moreover, Slik is necessary and sufficient for preventing physiologic JNK signaling-mediated cell death in development. Furthermore, introduction of STK10, the human ortholog of Slik, into Drosophila restores slik depletion-induced cell death and compromised tissue homeostasis. Lastly, knockdown of STK10 in human cancer cells also leads to JNK activation, which is cancelled by expression of Slik.

CONCLUSIONS

This study has uncovered an evolutionarily conserved role of Slik/STK10 in blocking JNK signaling, which is required for cell death inhibition and tissue homeostasis maintenance in development.

Drosophila Phosphatase of Regenerating Liver Is Critical for Photoreceptor Cell Polarity and Survival during Retinal Development

Establishing apicobasal polarity, involving intricate interactions among polarity regulators, is key for epithelial cell function. Though phosphatase of regenerating liver (PRL) proteins are implicated in diverse biological processes, including cancer, their developmental role remains unclear. In this study, we explore the role of Drosophila PRL (dPRL) in photoreceptor cell development. We reveal that dPRL, requiring a C-terminal prenylation motif, is highly enriched in the apical membrane of developing photoreceptor cells. Moreover, dPRL knockdown during retinal development results in adult Drosophila retinal degeneration, caused by hid-induced apoptosis. dPRL depletion also mislocalizes cell adhesion and polarity proteins like Armadillo, Crumbs, and DaPKC and relocates the basolateral protein, alpha subunit of Na⁺/K⁺-ATPase, to the presumed apical membrane. Importantly, this polarity disruption is not secondary to apoptosis, as suppressing hid expression does not rescue the polarity defect in dPRL-depleted photoreceptor cells. These findings underscore dPRL's crucial role in photoreceptor cell polarity and emphasize PRL's importance in establishing epithelial polarity and maintaining cell survival during retinal development, offering new insights into PRL's role in normal epithelium.

Myo-Inositol Reverses TGF-β1-Induced EMT in MCF-10A Non-Tumorigenic Breast Cells

Epithelial-Mesenchymal Transition (EMT), triggered by external and internal cues in several physiological and pathological conditions, elicits the transformation of epithelial cells into a mesenchymal-like phenotype. During EMT, epithelial cells lose cell-to-cell contact and acquire unusual motility/invasive capabilities. The associated architectural and functional changes destabilize the epithelial layer consistency, allowing cells to migrate and invade the surrounding tissues. EMT is a critical step in the progression of inflammation and cancer, often sustained by a main driving factor as the transforming growth factor-β1 (TGF-β1). Antagonizing EMT has recently gained momentum as an attractive issue in cancer treatment and metastasis prevention. Herein, we demonstrate the capability of myo-inositol (myo-Ins) to revert the EMT process induced by TGF-β1 on MCF-10A breast cells. Upon TGF-β1 addition, cells underwent a dramatic phenotypic transformation, as witnessed by structural (disappearance of the E-cadherin-β-catenin complexes and the emergence of a mesenchymal shape) and molecular modifications (increase in N-cadherin, Snai1, and vimentin), including the release of increased collagen and fibronectin. However, following myo-Ins, those changes were almost completely reverted. Inositol promotes the reconstitution of E-cadherin-β-catenin complexes, decreasing the expression of genes involved in EMT, while promoting the re-expression of epithelial genes (keratin-18 and E-cadherin). Noticeably, myo-Ins efficiently inhibits the invasiveness and migrating capability of TGF-β1 treated cells, also reducing the release of metalloproteinase (MMP-9) altogether with collagen synthesis, allowing for the re-establishment of appropriate cell-to-cell junctions, ultimately leading the cell layer back towards a more compact state. Inositol effects were nullified by previous treatment with an siRNA construct to inhibit CDH1 transcripts and, hence, E-cadherin synthesis. This finding suggests that the reconstitution of E-cadherin complexes is an irreplaceable step in the inositol-induced reversion of EMT. Overall, such a result advocates for the useful role of myo-Ins in cancer treatment.

Clonal interactions in cancer: integrating quantitative models with experimental and clinical data

Tumors consist of different genotypically distinct subpopulations-or subclones-of cells. These subclones can influence neighboring clones in a process called "clonal interaction." Conventionally, research on driver mutations in cancer has focused on their cell-autonomous effects that lead to an increase in fitness of the cells containing the driver. Recently, with the advent of improved experimental and computational technologies for investigating tumor heterogeneity and clonal dynamics, new studies have shown the importance of clonal interactions in cancer initiation, progression, and metastasis. In this review we provide an overview of clonal interactions in cancer, discussing key discoveries from a diverse range of approaches to cancer biology research. We discuss common types of clonal interactions, such as cooperation and competition, its mechanisms, and the overall effect on tumorigenesis, with important implications for tumor heterogeneity, resistance to treatment, and tumor suppression. Quantitative models-in coordination with cell culture and animal model experiments-have played a vital role in investigating the nature of clonal interactions and the complex clonal dynamics they generate. We present mathematical and computational models that can be used to represent clonal interactions and provide examples of the roles they have played in identifying and quantifying the strength of clonal interactions in experimental systems. Clonal interactions have proved difficult to observe in clinical data; however, several very recent quantitative approaches enable their detection. We conclude by discussing ways in which researchers can further integrate quantitative methods with experimental and clinical data to elucidate the critical-and often surprising-roles of clonal interactions in human cancers.

Cell polarity opposes Jak/STAT-mediated Escargot activation that drives intratumor heterogeneity in a Drosophila tumor model

In proliferating neoplasms, microenvironment-derived selective pressures promote tumor heterogeneity by imparting diverse capacities for growth, differentiation, and invasion. However, what makes a tumor cell respond to signaling cues differently from a normal cell is not well understood. In the Drosophila ovarian follicle cells, apicobasal-polarity loss induces heterogeneous epithelial multilayering. When exacerbated by oncogenic-Notch expression, this multilayer displays an increased consistency in the occurrence of morphologically distinguishable cells adjacent to the polar follicle cells. Polar cells release the Jak/STAT ligand Unpaired (Upd), in response to which neighboring polarity-deficient cells exhibit a precursor-like transcriptomic state. Among the several regulons active in these cells, we could detect and further validate the expression of Snail family transcription factor Escargot (Esg). We also ascertain a similar relationship between Upd and Esg in normally developing ovaries, where establishment of polarity determines early follicular differentiation. Overall, our results indicate that epithelial-cell polarity acts as a gatekeeper against microenvironmental selective pressures that drive heterogeneity.

Modelling Cancer Metastasis in Drosophila melanogaster

Cancer metastasis, the process by which tumour cells spread throughout the body and form secondary tumours at distant sites, is the leading cause of cancer-related deaths. The metastatic cascade is a highly complex process encompassing initial dissemination from the primary tumour, travel through the blood stream or lymphatic system, and the colonisation of distant organs. However, the factors enabling cells to survive this stressful process and adapt to new microenvironments are not fully characterised. Drosophila have proven a powerful system in which to study this process, despite important caveats such as their open circulatory system and lack of adaptive immune system. Historically, larvae have been used to model cancer due to the presence of pools of proliferating cells in which tumours can be induced, and transplanting these larval tumours into adult hosts has enabled tumour growth to be monitored over longer periods. More recently, thanks largely to the discovery that there are stem cells in the adult midgut, adult models have been developed. We focus this review on the development of different Drosophila models of metastasis and how they have contributed to our understanding of important factors determining metastatic potential, including signalling pathways, the immune system and the microenvironment.

Metastatic effects of environmental carcinogens mediated by MAPK and UPR pathways with an in vivo Drosophila Model

Metastasis includes tumor invasion and migration and underlies over 90% of cancer mortality. The metastatic effects of environmental carcinogens raised serious health concerns. However, the underlying mechanisms remained poorly studied. In the present study, an in vivo Ras^V12/lgl^-/- model of the fruitfly, Drosophila melanogaster, with an 8-day exposure was employed to explore the metastatic effects of 3,3',4,4',5-pentachlorobiphenyl (PCB126), perfluorooctanoic acid (PFOA) and cadmium chloride (CdCl₂). At 1.0 mg/L, PCB126, PFOA, and CdCl₂ significantly increased tumor invasion rates by 1.32-, 1.33-, and 1.29-fold of the control, respectively. They also decreased the larval body weight and locomotion behavior. Moreover, they commonly disturbed the expression levels of target genes in MAPK and UPR pathways, and their metastatic effects were significantly abolished by the addition of p38 inhibitor (SB203580), JNK inhibitor (SP600125) and IRE1 inhibitor (KIRA6). Notably, the addition of the IRE inhibitor significantly influenced sna/E-cad pathway which is essential in both p38 and JNK regulations. The results demonstrated an essential role of sna/E-cad in connecting the effects of carcinogens on UPR and MAPK regulations and the resultant metastasis.

Chitinase-like proteins promoting tumorigenesis through disruption of cell polarity via enlarged endosomal vesicles

Introduction

Chitinase-like proteins (CLPs) are associated with tissue-remodeling and inflammation but also with several disorders, including fibrosis, atherosclerosis, allergies, and cancer. However, CLP's role in tumors is far from clear.

Methods

Here, we utilize Drosophila melanogaster and molecular genetics to investigate the function of CLPs (imaginal disc growth factors; Idgf's) in Ras^V12 dysplastic salivary glands.

Results and discussion

We find one of the Idgf's members, Idgf3, is transcriptionally induced in a JNK-dependent manner via a positive feedback loop mediated by reactive oxygen species (ROS). Moreover, Idgf3 accumulates in enlarged endosomal vesicles (EnVs) that promote tumor progression by disrupting cytoskeletal organization. The process is mediated via the downstream component, aSpectrin, which localizes to the EnVs. Our data provide new insight into CLP function in tumors and identifies specific targets for tumor control.

Cell polarity and extrusion: How to polarize extrusion and extrude misspolarized cells?

The barrier function of epithelia is one of the cornerstones of the body plan organization of metazoans. It relies on the polarity of epithelial cells which organizes along the apico-basal axis the mechanical properties, signaling as well as transport. This barrier function is however constantly challenged by the fast turnover of epithelia occurring during morphogenesis or adult tissue homeostasis. Yet, the sealing property of the tissue can be maintained thanks to cell extrusion: a series of remodeling steps involving the dying cell and its neighbors leading to seamless cell expulsion. Alternatively, the tissue architecture can also be challenged by local damages or the emergence of mutant cells that may alter its organization. This includes mutants of the polarity complexes which can generate neoplastic overgrowths or be eliminated by cell competition when surrounded by wild type cells. In this review, we will provide an overview of the regulation of cell extrusion in various tissues focusing on the relationship between cell polarity, cell organization and the direction of cell expulsion. We will then describe how local perturbations of polarity can also trigger cell elimination either by apoptosis or by cell exclusion, focusing specifically on how polarity defects can be directly causal to cell elimination. Overall, we propose a general framework connecting the influence of polarity on cell extrusion and its contribution to aberrant cell elimination.

Biochemical and clinical effects of RPS20 expression in renal clear cell carcinoma

Renal cell carcinoma (RCC) remains one of the most lethal urinary tumors in East Asia despite great advancements in treatment strategies in recent years. Ribosomal protein S20 (RPS20) is considered a new oncogene; however, little information is available on its expression, regulation and biological function in patients with RCC. In the present study, 43 pairs of human RCC and neighboring normal renal tissues were examined for protein expression and immunohistochemistry examination of RPS20. Lentiviral transduction was also employed to create RPS20 knockdown cell lines for downstream cellular experiments. MTT, flow cytometry, wound healing, colony formation and invasion assays were used to examine how RPS20 affected kidney renal clear cell carcinoma (KIRC) cell behavior. Western blotting was used to detect cycle‑related proteins (CDK4 and cyclin D1), Wnt‑related proteins (N‑cadherin and E‑cadherin) and signaling proteins [phosphorylated (p)‑AKT and p‑ERK]. The functions of RPS20 in vivo were examined in 786‑O cells with RPS20 knockdown. RPS20 was significantly overexpressed in tumor tissues compared with its expression in the corresponding normal tissues. RPS20 expression was linked to tumor stage, differentiation grade, tumor size and lymph node metastasis, and it had an independent prognostic value in KIRC. Since RCC cell proliferation, migration and invasion were suppressed when RPS20 was knocked down, the formation of renal tumors in vivo was markedly slowed down. In RPS20 knockdown cell lines, CDK4, cyclin D1 and E‑cadherin were downregulated, while N‑cadherin expression was increased. RPS20 was also observed to be involved in controlling the activation of the ERK and mTOR signaling pathways. In summary, the present study showed that RPS20 increased cell proliferation in RCC by activating the AKT‑mTOR and ERK‑MAPK signaling pathways, which suggests that RPS20 may be a therapeutic and prognostic target for RCC.

Cell-cell interactions that drive tumorigenesis in Drosophila

Cell-cell interactions within tumour microenvironment play crucial roles in tumorigenesis. Genetic mosaic techniques available in Drosophila have provided a powerful platform to study the basic principles of tumour growth and progression via cell-cell communications. This led to the identification of oncogenic cell-cell interactions triggered by endocytic dysregulation, mitochondrial dysfunction, cell polarity defects, or Src activation in Drosophila imaginal epithelia. Such oncogenic cooperations can be caused by interactions among epithelial cells, mesenchymal cells, and immune cells. Moreover, microenvironmental factors such as nutrients, local tissue structures, and endogenous growth signalling activities critically affect tumorigenesis. Dissecting various types of oncogenic cell-cell interactions at the single-cell level in Drosophila will greatly increase our understanding of how tumours progress in living animals.

The CRL4 E3 ligase Mahjong/DCAF1 controls cell competition through the transcription factor Xrp1, independently of polarity genes

Cell competition, the elimination of cells surrounded by more fit neighbors, is proposed to suppress tumorigenesis. Mahjong (Mahj), a ubiquitin E3 ligase substrate receptor, has been thought to mediate competition of cells mutated for lethal giant larvae (lgl), a neoplastic tumor suppressor that defines apical-basal polarity of epithelial cells. Here, we show that Drosophila cells mutated for mahjong, but not for lgl [l(2)gl], are competed because they express the bZip-domain transcription factor Xrp1, already known to eliminate cells heterozygous for ribosomal protein gene mutations (Rp/+ cells). Xrp1 expression in mahj mutant cells results in activation of JNK signaling, autophagosome accumulation, eIF2α phosphorylation and lower translation, just as in Rp/+ cells. Cells mutated for damage DNA binding-protein 1 (ddb1; pic) or cullin 4 (cul4), which encode E3 ligase partners of Mahj, also display Xrp1-dependent phenotypes, as does knockdown of proteasome subunits. Our data suggest a new model of mahj-mediated cell competition that is independent of apical-basal polarity and couples Xrp1 to protein turnover.

A Scribble/Cdep/Rac pathway controls follower-cell crawling and cluster cohesion during collective border-cell migration

Collective cell movements drive normal development and metastasis. Drosophila border cells move as a cluster of 6-10 cells, where the role of the Rac GTPase in migration was first established. In border cells, as in most migratory cells, Rac stimulates leading-edge protrusion. Upstream Rac regulators in leaders have been identified; however, the regulation and function of Rac in follower border cells is unknown. Here, we show that all border cells require Rac, which promotes follower-cell motility and is important for cluster compactness and movement. We identify a Rac guanine nucleotide exchange factor, Cdep, which also regulates follower-cell movement and cluster cohesion. Scribble, Discs large, and Lethal giant larvae localize Cdep basolaterally and share phenotypes with Cdep. Relocalization of Cdep::GFP partially rescues Scribble knockdown, suggesting that Cdep is a major downstream effector of basolateral proteins. Thus, a Scrib/Cdep/Rac pathway promotes cell crawling and coordinated, collective migration in vivo.

Single-cell transcriptomics identifies Keap1-Nrf2 regulated collective invasion in a Drosophila tumor model

Apicobasal cell polarity loss is a founding event in epithelial-mesenchymal transition and epithelial tumorigenesis, yet how pathological polarity loss links to plasticity remains largely unknown. To understand the mechanisms and mediators regulating plasticity upon polarity loss, we performed single-cell RNA sequencing of Drosophila ovaries, where inducing polarity-gene l(2)gl-knockdown (Lgl-KD) causes invasive multilayering of the follicular epithelia. Analyzing the integrated Lgl-KD and wildtype transcriptomes, we discovered the cells specific to the various discernible phenotypes and characterized the underlying gene expression. A genetic requirement of Keap1-Nrf2 signaling in promoting multilayer formation of Lgl-KD cells was further identified. Ectopic expression of Keap1 increased the volume of delaminated follicle cells that showed enhanced invasive behavior with significant changes to the cytoskeleton. Overall, our findings describe the comprehensive transcriptome of cells within the follicle cell tumor model at the single-cell resolution and identify a previously unappreciated link between Keap1-Nrf2 signaling and cell plasticity at early tumorigenesis.

Drosophila hemocytes recognize lymph gland tumors of mxc mutants and activate the innate immune pathway in a reactive oxygen species-dependent manner

Mechanisms of cancer cell recognition and elimination by the innate immune system remains unclear. The immune signaling pathways are activated in the fat body to suppress the tumor growth in mxcmbn1 hematopoietic tumor mutants in Drosophila by inducing antimicrobial peptides (AMP). Here, we investigated the regulatory mechanism underlying the activation in the mutant. Firstly, we found that reactive oxygen species (ROS) accumulated in the hemocytes due to induction of dual oxidase and one of its activators. This was required for the AMP induction and the tumor growth suppression. Next, more hemocytes transplanted from normal larvae were associated with the mutant tumor than normal lymph glands (LGs). Matrix metalloproteinase 1 and 2 (MMP2) were highly expressed in the tumors. The basement membrane components in the tumors were reduced and ultimately lost inside. Depletion of the MMP2 rather than MMP1 resulted in a significantly reduced AMP expression in the mutant larvae. The hemocytes may recognize the disassembly of basement membrane in the tumors and activate the ROS production. Our findings highlight the mechanism via which macrophage-like hemocytes recognize tumor cells and subsequently convey the information to induce AMPs in the fat body. They contribute to uncover the role of innate immune system against cancer.

Analysis of the Anti-Tumour Effect of Xuefu Zhuyu Decoction Based on Network Pharmacology and Experimental Verification in Drosophila

Background: Tumours are among the most lethal diseases that heavily endanger human health globally. Xuefu Zhuyu Decoction (XFZYD) is a prescription used to treat blood-activating stasis. Although XFZYD has been shown to suppress migration and invasion of tumour cells, the active ingredients, potential targets, and underlying mechanism remain largely elusive. Purpose: To identify the prospective ingredients and major targets of XFZYD against tumours, and evaluate the efficacy and potential molecular mechanisms of XFZYD extract on tumour growth and invasion. Methods: We predicted that XFZYD might act on 80 targets through 128 active components using the network pharmacology analysis method. In addition, we prepared an XFZYD aqueous extract and employed the RasV12/lgl -/- -induced Drosophila tumour model to carry out experimental verification. Results: XFZYD did not exhibit any side effects on development, viability, and fertility. Furthermore, XFZYD significantly impeded tumour size and invasion at moderate concentrations and suppressed the increased phosphorylation of JNK but strongly enhanced the expression of Caspase 3 in the RasV12/lgl -/- model. Finally, the mRNA level of the transcription complex AP-1 component c-FOS was remarkably reduced. In contrast, the transcription of three pro-apoptotic genes was significantly increased when XFZYD was used to treat the tumour model. Conclusion: The study findings suggest that XFZYD may promote tumour cell apoptosis by activating caspase signalling to control primary growth and hinder tumour cell invasion by suppressing JNK/AP-1 signalling activity, thus providing a potential therapeutic strategy for XFZYD in the clinical treatment of cancer and other related diseases.

Drosophila Innate Immunity Involves Multiple Signaling Pathways and Coordinated Communication Between Different Tissues

The innate immune response provides the first line of defense against invading pathogens, and immune disorders cause a variety of diseases. The fruit fly Drosophila melanogaster employs multiple innate immune reactions to resist infection. First, epithelial tissues function as physical barriers to prevent pathogen invasion. In addition, macrophage-like plasmatocytes eliminate intruders through phagocytosis, and lamellocytes encapsulate large particles, such as wasp eggs, that cannot be phagocytosed. Regarding humoral immune responses, the fat body, equivalent to the mammalian liver, secretes antimicrobial peptides into hemolymph, killing bacteria and fungi. Drosophila has been shown to be a powerful in vivo model for studying the mechanism of innate immunity and host-pathogen interactions because Drosophila and higher organisms share conserved signaling pathways and factors. Moreover, the ease with which Drosophila genetic and physiological characteristics can be manipulated prevents interference by adaptive immunity. In this review, we discuss the signaling pathways activated in Drosophila innate immunity, namely, the Toll, Imd, JNK, JAK/STAT pathways, and other factors, as well as relevant regulatory networks. We also review the mechanisms by which different tissues, including hemocytes, the fat body, the lymph gland, muscles, the gut and the brain coordinate innate immune responses. Furthermore, the latest studies in this field are outlined in this review. In summary, understanding the mechanism underlying innate immunity orchestration in Drosophila will help us better study human innate immunity-related diseases.

Two types of critical cell density for mechanical elimination of abnormal cell clusters from epithelial tissue

Recent technological advances in high-resolution imaging and artificial modulation of genetic functions at different times and regions have enabled direct observations of the formation and elimination of abnormal cell populations. A recent trend in cell competition research is the incorporation of cell mechanics. In different tissues and species, abnormal cells developing in epithelial tissues are mechanically eliminated by cell contraction via actomyosin accumulation at the interface between normal and abnormal cells. This mechanical cell elimination process has attracted attention as a potential universal defense mechanism. Here, we theoretically examined the conditions for mechanical elimination of growing abnormal cell populations. Simulations and mathematical analyses using a vertex dynamics model revealed two types of critical cell density associated with mechanical elimination of abnormal cell clusters. One is a subtype of homeostatic density, in which the frequencies of spontaneous mechanical cell elimination and proliferation are balanced, even if no explicit dependence of proliferation or apoptosis on the cell density is assumed. This density is related to the mechanical stability of a single cell. The other is density related to mechanical stability as a cell population under external pressure. Both density types are determined by tissue mechanical properties. In solid tissues, the former type is reached first as the intensity of interfacial contraction increases, and it functions as a critical density. On the other hand, the latter type becomes critical when tissues are highly fluid. The derived analytical solution explicitly reveals the dependence of critical contractile force and density on different parameters. We also found a negative correlation between the proliferation rate of abnormal cells and the likelihood of the abnormal cell population expanding by escaping elimination. This is counterintuitive because in the context of cell competition, fast-growing cell populations generally win. These findings provide new insight into, and interpretation of, the results from experimental studies.

High-resolution imaging techniques have revealed that abnormal cells developing in epithelial tissues are mechanically eliminated via contraction at the interface between the abnormal cells and normal surrounding cells. This phenomenon is seen in various species and tissues and thus is regarded as a primitive defense system against precancerous cells common to all animals. For comprehensive understanding of this potential defense system, we derived mathematical conditions to achieve mechanical elimination of growing abnormal cell populations. We identified two characteristic cell density types associated with successful mechanical elimination of abnormal cell clusters. Both are determined by tissue physical properties, and the smaller of the two functions as a critical density above which abnormal cell populations cannot exist. We also found a counterintuitive phenomenon in which slower proliferation of abnormal cells promotes their growth as a population. Our results will help elucidate the mechanisms of intrinsic tissue defenses against cancer from the perspective of cell mechanics.

Endocytosis at the Crossroad of Polarity and Signaling Regulation: Learning from Drosophila melanogaster and Beyond

Cellular trafficking through the endosomal–lysosomal system is essential for the transport of cargo proteins, receptors and lipids from the plasma membrane inside the cells and across membranous organelles. By acting as sorting stations, vesicle compartments direct the fate of their content for degradation, recycling to the membrane or transport to the trans-Golgi network. To effectively communicate with their neighbors, cells need to regulate their compartmentation and guide their signaling machineries to cortical membranes underlying these contact sites. Endosomal trafficking is indispensable for the polarized distribution of fate determinants, adaptors and junctional proteins. Conversely, endocytic machineries cooperate with polarity and scaffolding components to internalize receptors and target them to discrete membrane domains. Depending on the cell and tissue context, receptor endocytosis can terminate signaling responses but can also activate them within endosomes that act as signaling platforms. Therefore, cell homeostasis and responses to environmental cues rely on the dynamic cooperation of endosomal–lysosomal machineries with polarity and signaling cues. This review aims to address advances and emerging concepts on the cooperative regulation of endocytosis, polarity and signaling, primarily in Drosophila melanogaster and discuss some of the open questions across the different cell and tissue types that have not yet been fully explored.

Extracellular ATP facilitates cell extrusion from epithelial layers mediated by cell competition or apoptosis

For the maintenance of epithelial homeostasis, various aberrant or dysfunctional cells are actively eliminated from epithelial layers. This cell extrusion process mainly falls into two modes: cell-competition-mediated extrusion and apoptotic extrusion. However, it is not clearly understood whether and how these processes are governed by common molecular mechanisms. In this study, we demonstrate that the reactive oxygen species (ROS) levels are elevated within a wide range of epithelial layers around extruding transformed or apoptotic cells. The downregulation of ROS suppresses the extrusion process. Furthermore, ATP is extracellularly secreted from extruding cells, which promotes the ROS level and cell extrusion. Moreover, the extracellular ATP and ROS pathways positively regulate the polarized movements of surrounding cells toward extruding cells in both cell-competition-mediated and apoptotic extrusion. Hence, extracellular ATP acts as an "extrude me" signal and plays a prevalent role in cell extrusion, thereby sustaining epithelial homeostasis and preventing pathological conditions or disorders.

Metastasis and MAPK Pathways

Cancer is a leading cause of death worldwide. In many cases, the treatment of the disease is limited due to the metastasis of cells to distant locations of the body through the blood and lymphatic drainage. Most of the anticancer therapeutic options focus mainly on the inhibition of tumor cell growth or the induction of cell death, and do not consider the molecular basis of metastasis. The aim of this work is to provide a comprehensive review focusing on cancer metastasis and the mitogen-activated protein kinase (MAPK) pathway (ERK/JNK/P38 signaling) as a crucial modulator of this process.

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

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

TSPAN6 is a suppressor of Ras-driven cancer

Oncogenic mutations in the small GTPase RAS contribute to ~30% of human cancers. In a Drosophila genetic screen, we identified novel and evolutionary conserved cancer genes that affect Ras-driven tumorigenesis and metastasis in Drosophila including confirmation of the tetraspanin Tsp29Fb. However, it was not known whether the mammalian Tsp29Fb orthologue, TSPAN6, has any role in RAS-driven human epithelial tumors. Here we show that TSPAN6 suppressed tumor growth and metastatic dissemination of human RAS activating mutant pancreatic cancer xenografts. Whole-body knockout as well as tumor cell autonomous inactivation using floxed alleles of Tspan6 in mice enhanced Kras^G12D-driven lung tumor initiation and malignant progression. Mechanistically, TSPAN6 binds to the EGFR and blocks EGFR-induced RAS activation. Moreover, we show that inactivation of TSPAN6 induces an epithelial-to-mesenchymal transition and inhibits cell migration in vitro and in vivo. Finally, low TSPAN6 expression correlates with poor prognosis of patients with lung and pancreatic cancers with mesenchymal morphology. Our results uncover TSPAN6 as a novel tumor suppressor receptor that controls epithelial cell identify and restrains RAS-driven epithelial cancer.

Mechanisms underlying the cooperation between loss of epithelial polarity and Notch signaling during neoplastic growth in Drosophila

Aggressive neoplastic growth can be initiated by a limited number of genetic alterations, such as the well-established cooperation between loss of cell architecture and hyperactive signaling pathways. However, our understanding of how these different alterations interact and influence each other remains very incomplete. Using Drosophila paradigms of imaginal wing disc epithelial growth, we have monitored the changes in Notch pathway activity according to the polarity status of cells (scrib mutant). We show that the scrib mutation impacts the direct transcriptional output of the Notch pathway, without altering the global distribution of Su(H), the Notch-dedicated transcription factor. The Notch-dependent neoplasms require, however, the action of a group of transcription factors, similar to those previously identified for Ras/scrib neoplasm (namely AP-1, Stat92E, Ftz-F1 and basic leucine zipper factors), further suggesting the importance of this transcription factor network during neoplastic growth. Finally, our work highlights some Notch/scrib specificities, in particular the role of the PAR domain-containing basic leucine zipper transcription factor and Notch direct target Pdp1 for neoplastic growth.

Toll-7 promotes tumour growth and invasion in Drosophila

Objectives

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

Materials and methods

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

Results

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

Conclusions

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

AVL9 promotes colorectal carcinoma cell migration via regulating EGFR expression

Background

Despite advanced treatments could inhibit progression of colorectal carcinoma (CRC), the recurrence and metastasis remain challenging issues. Accumulating evidences implicated that AVL9 played a vital role in human cancers, but it’s biological function and mechanism in CRC remain unclear.

Aim

To investigate the biological role and mechanism of AVL9 in colorectal carcinoma.

Results

AVL9 expression was significantly upregulated in tumor tissues than that in matched normal tissues both at mRNA and protein levels. High expression of AVL9 was closely correlated with M status, stages and poor prognosis of colorectal carcinoma (CRC) patients. Functionally, AVL9 overexpression promoted cell migration rather than cell proliferation in vitro, whereas AVL9 knockdown exhibited the contrary results. Mechanistically, AVL9 regulated EGFR expression, and knockdown of EGFR restrained AVL9-induced cell migration.

Conclusion

These findings demonstrated that AVL9 contributed to CRC cell migration by regulating EGFR expression, suggesting a potential biomarker and treatment target for CRC.

PTP61F Mediates Cell Competition and Mitigates Tumorigenesis

Tissue homeostasis via the elimination of aberrant cells is fundamental for organism survival. Cell competition is a key homeostatic mechanism, contributing to the recognition and elimination of aberrant cells, preventing their malignant progression and the development of tumors. Here, using Drosophila as a model organism, we have defined a role for protein tyrosine phosphatase 61F (PTP61F) (orthologue of mammalian PTP1B and TCPTP) in the initiation and progression of epithelial cancers. We demonstrate that a Ptp61F null mutation confers cells with a competitive advantage relative to neighbouring wild-type cells, while elevating PTP61F levels has the opposite effect. Furthermore, we show that knockdown of Ptp61F affects the survival of clones with impaired cell polarity, and that this occurs through regulation of the JAK-STAT signalling pathway. Importantly, PTP61F plays a robust non-cell-autonomous role in influencing the elimination of adjacent polarity-impaired mutant cells. Moreover, in a neoplastic RAS-driven polarity-impaired tumor model, we show that PTP61F levels determine the aggressiveness of tumors, with Ptp61F knockdown or overexpression, respectively, increasing or reducing tumor size. These effects correlate with the regulation of the RAS-MAPK and JAK-STAT signalling by PTP61F. Thus, PTP61F acts as a tumor suppressor that can function in an autonomous and non-cell-autonomous manner to ensure cellular fitness and attenuate tumorigenesis.

A Blueprint for Cancer-Related Inflammation and Host Innate Immunity

Both in situ and allograft models of cancer in juvenile and adult Drosophila melanogaster fruit flies offer a powerful means for unravelling cancer gene networks and cancer-host interactions. They can also be used as tools for cost-effective drug discovery and repurposing. Moreover, in situ modeling of emerging tumors makes it possible to address cancer initiating events-a black box in cancer research, tackle the innate antitumor immune responses to incipient preneoplastic cells and recurrent growing tumors, and decipher the initiation and evolution of inflammation. These studies in Drosophila melanogaster can serve as a blueprint for studies in more complex organisms and help in the design of mechanism-based therapies for the individualized treatment of cancer diseases in humans. This review focuses on new discoveries in Drosophila related to the diverse innate immune responses to cancer-related inflammation and the systemic effects that are so detrimental to the host.

JNK and Yorkie drive tumor malignancy by inducing L-amino acid transporter 1 in Drosophila

Identifying a common oncogenesis pathway among tumors with different oncogenic mutations is critical for developing anti-cancer strategies. Here, we performed transcriptome analyses on two different models of Drosophila malignant tumors caused by Ras activation with cell polarity defects (RasV12/scrib-/-) or by microRNA bantam overexpression with endocytic defects (bantam/rab5-/-), followed by an RNAi screen for genes commonly essential for tumor growth and malignancy. We identified that Juvenile hormone Inducible-21 (JhI-21), a Drosophila homolog of the L-amino acid transporter 1 (LAT1), is upregulated in these malignant tumors with different oncogenic mutations and knocking down of JhI-21 strongly blocked their growth and invasion. JhI-21 expression was induced by simultaneous activation of c-Jun N-terminal kinase (JNK) and Yorkie (Yki) in these tumors and thereby contributed to tumor growth and progression by activating the mTOR-S6 pathway. Pharmacological inhibition of LAT1 activity in Drosophila larvae significantly suppressed growth of RasV12/scrib-/- tumors. Intriguingly, LAT1 inhibitory drugs did not suppress growth of bantam/rab5-/- tumors and overexpression of bantam rendered RasV12/scrib-/- tumors unresponsive to LAT1 inhibitors. Further analyses with RNA sequencing of bantam-expressing clones followed by an RNAi screen suggested that bantam induces drug resistance against LAT1 inhibitors via downregulation of the TMEM135-like gene CG31157. Our observations unveil an evolutionarily conserved role of LAT1 induction in driving Drosophila tumor malignancy and provide a powerful genetic model for studying cancer progression and drug resistance.

Drosophila melanogaster: A Powerful Tiny Animal Model for the Study of Metabolic Hepatic Diseases

Animal experimentation is limited by unethical procedures, time-consuming protocols, and high cost. Thus, the development of innovative approaches for disease treatment based on alternative models in a fast, safe, and economic manner is an important, yet challenging goal. In this paradigm, the fruit-fly Drosophila melanogaster has become a powerful model for biomedical research, considering its short life cycle and low-cost maintenance. In addition, biological processes are conserved and homologs of ∼75% of human disease-related genes are found in the fruit-fly. Therefore, this model has been used in innovative approaches to evaluate and validate the functional activities of candidate molecules identified via in vitro large-scale analyses, as putative agents to treat or reverse pathological conditions. In this context, Drosophila offers a powerful alternative to investigate the molecular aspects of liver diseases, since no effective therapies are available for those pathologies. Non-alcoholic fatty liver disease is the most common form of chronic hepatic dysfunctions, which may progress to the development of chronic hepatitis and ultimately to cirrhosis, thereby increasing the risk for hepatocellular carcinoma (HCC). This deleterious situation reinforces the use of the Drosophila model to accelerate functional research aimed at deciphering the mechanisms that sustain the disease. In this short review, we illustrate the relevance of using the fruit-fly to address aspects of liver pathologies to contribute to the biomedical area.