JNK- and Fos-regulated Mmp1 expression cooperates with Ras to induce invasive tumors in Drosophila

Immune response to bacteria induces dissemination of Ras-activated Drosophila hindgut cells

Although pathogenic bacteria are suspected contributors to colorectal cancer progression, cancer-promoting bacteria and their mode of action remain largely unknown. Here we report that sustained infection with the human intestinal colonizer Pseudomonas aeruginosa synergizes with the Ras1V12 oncogene to induce basal invasion and dissemination of hindgut cells to distant sites. Cross-talk between infection and dissemination requires sustained activation by the bacteria of the Imd-dTab2-dTak1 innate immune pathway, which converges with Ras1V12 signalling on JNK pathway activation, culminating in extracellular matrix degradation. Hindgut, but not midgut, cells are amenable to this cooperative dissemination, which is progressive and genetically and pharmacologically inhibitable. Thus, Drosophila hindgut provides a valuable system for the study of intestinal malignancies.

Notch and Mef2 synergize to promote proliferation and metastasis through JNK signal activation in Drosophila

Genetic analyses in Drosophila revealed a synergy between Notch and the pleiotropic transcription factor Mef2 (myocyte enhancer factor 2), which profoundly influences proliferation and metastasis. We show that these hyperproliferative and invasive Drosophila phenotypes are attributed to upregulation of eiger, a member of the tumour necrosis factor superfamily of ligands, and the consequent activation of Jun N-terminal kinase signalling, which in turn triggers the expression of the invasive marker MMP1. Expression studies in human breast tumour samples demonstrate correlation between Notch and Mef2 paralogues and support the notion that Notch-MEF2 synergy may be significant for modulating human mammary oncogenesis.

raw Functions through JNK signaling and cadherin-based adhesion to regulate Drosophila gonad morphogenesis

To form a gonad, germ cells (GCs) and somatic gonadal precursor cells (SGPs) must migrate to the correct location in the developing embryo and establish the cell-cell interactions necessary to create proper gonad architecture. During gonad morphogenesis, SGPs send out cellular extensions to ensheath the individual GCs and promote their development. We have identified mutations in the raw gene that result in a failure of the SGPs to ensheath the GCs, leading to defects in GC development. Using genetic analysis and gene expression studies, we find that Raw negatively regulates JNK signaling during gonad morphogenesis, and increased JNK signaling is sufficient to cause ensheathment defects. In particular, Raw functions upstream of the Drosophila Jun-related transcription factor to regulate its subcellular localization. Since JNK signaling regulates cell adhesion during the morphogenesis of many tissues, we examined the relationship between raw and the genes encoding Drosophila E-cadherin and β-catenin, which function together in cell adhesion. We find that loss of DE-cadherin strongly enhances the raw mutant gonad phenotype, while increasing DE-cadherin function rescues this phenotype. Further, loss of raw results in mislocalization of β-catenin away from the cell surface. Therefore, cadherin-based cell adhesion, likely at the level of β-catenin, is a primary mechanism by which Raw regulates germline-soma interaction.

A secreted MMP is required for reepithelialization during wound healing

Matrix metalloproteinases (MMPs) are extracellular proteases highly expressed at wound sites. However, the precise function of MMPs during reepithelialization in vivo has been elusive in mammalian models because of the high level of redundancy among the 24 mammalian MMPs. For this reason we used Drosophila melanogaster, whose genome encodes only two MMPs-one secreted type (Mmp1) and one membrane-anchored type (Mmp2)-to study the function and regulation of the secreted class of MMPs in vivo. In the absence of redundancy, we found that the Drosophila secreted MMP, Mmp1, is required in the epidermis to facilitate reepithelialization by remodeling the basement membrane, promoting cell elongation and actin cytoskeletal reorganization, and activating extracellular signal-regulated kinase signaling. In addition, we report that the jun N-terminal kinase (JNK) pathway upregulates Mmp1 expression after wounding, but that Mmp1 is expressed independent of the JNK pathway in unwounded epidermis. When the JNK pathway is ectopically activated to overexpress Mmp1, the rate of healing is accelerated in an Mmp1-dependent manner. A primary function of Mmp1, under the control of the JNK pathway, is to promote basement membrane repair, which in turn may permit cell migration and the restoration of a continuous tissue.

Drosophila endocytic neoplastic tumor suppressor genes regulate Sav/Wts/Hpo signaling and the c-Jun N-terminal kinase pathway

Genetic screens in the fruit fly Drosophila melanogaster have identified a class of neoplastic tumor suppressor genes (endocytic nTSGs), which encode proteins that localize to endosomes and facilitate the trafficking of membrane-bound receptors and adhesion molecules into the degradative lysosome. Loss of endocytic nTSGs transforms imaginal disc epithelia into highly proliferative, invasive tissues that fail to differentiate and display defects in cellular apicobasal polarity, adhesion and tissue architecture. As vertebrate homologs of some Drosophila nTSGs are linked to tumor formation, identifying molecular changes in signaling associated with nTSG loss could inform understanding of neoplastic transformation in vertebrates. Here we show that mutations in genes that act at multiple steps of the endolysosomal pathway lead to autonomous activation of the Sav/Wts/Hpo (SWH) transcriptional effector Yki (YAP/TAZ in vertebrates) and the Jun N-terminal kinase (JNK), which is known to promote Yki activity in cells with disrupted polarity. Yki and JNK activity are elevated by mutations at multiple steps in the endolysosomal pathway including mutations in the AP-2σ gene, which encodes a component of the AP-2 adaptor complex that recruits cargoes into clathrin-coated pits for subsequent internalization. Moreover, reduction of JNK activity can decrease elevated Yki-signaling caused by altered endocytosis. These studies reveal a broad requirement for components of the endocytic pathway in regulating SWH and JNK outputs, and place Drosophila endocytic nTSGs into a network that involving two major signaling pathways implicated in oncogenesis.

Drosophila cancer models

Cancer is driven by complex genetic and cellular mechanisms. Recently, the Drosophila community has become increasingly interested in exploring cancer issues. The Drosophila field has made seminal contributions to many of the mechanisms that are fundamental to the cancer process; several of these mechanisms have already been validated in vertebrates. Less well known are the Drosophila field's early direct contributions to the cancer field: some of the earliest tumor suppressors were identified in flies. In this review, we identify major contributions that Drosophila studies have made toward dissecting the pathways and mechanisms underlying tumor progression. We also highlight areas, such as drug discovery, where we expect Drosophila studies to make a major scientific impact in the future.

Cell polarity and migration: emerging role for the endosomal sorting machinery

The endosomal sorting complex required for transport (ESCRT) machinery has been implicated in the regulation of endosomal sorting, cell division, viral budding, autophagy, and cell signaling. Here, we review recent evidence that implicates ESCRTs in cell polarity and cell migration, and discuss the potential role of ESCRTs as tumor suppressors.

Modeling tumor invasion and metastasis in Drosophila

Conservation of major signaling pathways between humans and flies has made Drosophila a useful model organism for cancer research. Our understanding of the mechanisms regulating cell growth, differentiation and development has been considerably advanced by studies in Drosophila. Several recent high profile studies have examined the processes constraining the metastatic growth of tumor cells in fruit fly models. Cell invasion can be studied in the context of an in vivo setting in flies, enabling the genetic requirements of the microenvironment of tumor cells undergoing metastasis to be analyzed. This Perspective discusses the strengths and limitations of Drosophila models of cancer invasion and the unique tools that have enabled these studies. It also highlights several recent reports that together make a strong case for Drosophila as a system with the potential for both testing novel concepts in tumor progression and cell invasion, and for uncovering players in metastasis.

Loss of the Drosophila cell polarity regulator Scribbled promotes epithelial tissue overgrowth and cooperation with oncogenic Ras-Raf through impaired Hippo pathway signaling

Background

Epithelial neoplasias are associated with alterations in cell polarity and excessive cell proliferation, yet how these neoplastic properties are related to one another is still poorly understood. The study of Drosophila genes that function as neoplastic tumor suppressors by regulating both of these properties has significant potential to clarify this relationship.

Results

Here we show in Drosophila that loss of Scribbled (Scrib), a cell polarity regulator and neoplastic tumor suppressor, results in impaired Hippo pathway signaling in the epithelial tissues of both the eye and wing imaginal disc. scrib mutant tissue overgrowth, but not the loss of cell polarity, is dependent upon defective Hippo signaling and can be rescued by knockdown of either the TEAD/TEF family transcription factor Scalloped or the transcriptional coactivator Yorkie in the eye disc, or reducing levels of Yorkie in the wing disc. Furthermore, loss of Scrib sensitizes tissue to transformation by oncogenic Ras-Raf signaling, and Yorkie-Scalloped activity is required to promote this cooperative tumor overgrowth. The inhibition of Hippo signaling in scrib mutant eye disc clones is not dependent upon JNK activity, but can be significantly rescued by reducing aPKC kinase activity, and ectopic aPKC activity is sufficient to impair Hippo signaling in the eye disc, even when JNK signaling is blocked. In contrast, warts mutant overgrowth does not require aPKC activity. Moreover, reducing endogenous levels of aPKC or increasing Scrib or Lethal giant larvae levels does not promote increased Hippo signaling, suggesting that aPKC activity is not normally rate limiting for Hippo pathway activity. Epistasis experiments suggest that Hippo pathway inhibition in scrib mutants occurs, at least in part, downstream or in parallel to both the Expanded and Fat arms of Hippo pathway regulation.

Conclusions

Loss of Scrib promotes Yorkie/Scalloped-dependent epithelial tissue overgrowth, and this is also important for driving cooperative tumor overgrowth with oncogenic Ras-Raf signaling. Whether this is also the case in human cancers now warrants investigation since the cell polarity function of Scrib and its capacity to restrain oncogene-mediated transformation, as well as the tissue growth control function of the Hippo pathway, are conserved in mammals.

Drosophila as a model of wound healing and tissue regeneration in vertebrates

Understanding the molecular basis of wound healing and regeneration in vertebrates is one of the main challenges in biology and medicine. This understanding will lead to medical advances allowing accelerated tissue repair after wounding, rebuilding new tissues/organs and restoring homeostasis. Drosophila has emerged as a valuable model for studying these processes because the genetic networks and cytoskeletal machinery involved in epithelial movements occurring during embryonic dorsal closure, larval imaginal disc fusion/regeneration, and epithelial repair are similar to those acting during wound healing and regeneration in vertebrates. Recent studies have also focused on the use of Drosophila adult stem cells to maintain tissue homeostasis. Here, we review how Drosophila has contributed to our understanding of these processes, primarily through live-imaging and genetic tools that are impractical in mammals. Furthermore, we highlight future research areas where this insect may provide novel insights and potential therapeutic strategies for wound healing and regeneration.

The transcription factor HLH-2/E/Daughterless regulates anchor cell invasion across basement membrane in C. elegans

Cell invasion through basement membrane is a specialized cellular behavior critical for many developmental processes and leukocyte trafficking. Invasive cellular behavior is also inappropriately co-opted during cancer progression. Acquisition of an invasive phenotype is accompanied by changes in gene expression that are thought to coordinate the steps of invasion. The transcription factors responsible for these changes in gene expression, however, are largely unknown. C. elegans anchor cell (AC) invasion is a genetically tractable in vivo model of invasion through basement membrane. AC invasion requires the conserved transcription factor FOS-1A, but other transcription factors are thought to act in parallel to FOS-1A to control invasion. Here we identify the transcription factor HLH-2, the C. elegans ortholog of Drosophila Daughterless and vertebrate E proteins, as a regulator of AC invasion. Reduction of HLH-2 function by RNAi or with a hypomorphic allele causes defects in AC invasion. Genetic analysis indicates that HLH-2 has functions outside of the FOS-1A pathway. Using expression analysis, we identify three genes that are transcriptionally regulated by HLH-2: the protocadherin cdh-3, and two genes encoding secreted extracellular matrix proteins, mig-6/papilin and him-4/hemicentin. Further, we show that reduction of HLH-2 function causes defects in polarization of F-actin to the invasive cell membrane, a process required for the AC to generate protrusions that breach the basement membrane. This work identifies HLH-2 as a regulator of the invasive phenotype in the AC, adding to our understanding of the transcriptional networks that control cell invasion.

Epithelial delamination and migration: lessons from Drosophila

Metastasis is the most deadly phase of cancer progression, during which cells detach from their original niche to invade distant tissues, yet the biological processes underlying the spread of cancer are still poorly understood. The fruit fly Drosophila melanogaster provides important insights in our understanding of how epithelial cells migrate from their original location and find their way into surrounding and distant tissues in the metastatic process. Here we review recent studies on the mechanisms of migration of embryonic haemocytes, the macrophage-like immuno-surveillance cells, during normal development and wound healing. We highlight the interesting finding that hydrogen peroxide (H₂O₂) has been identified as the driving force for haemocyte chemotaxis. We also give a special emphasis to studies suggesting the concept that haemocytes, together with the tumor microenvironment, act as potential inducers of the epithelial de-lamination required for tumor invasion. We propose that cell delamination and migration could be uncoupled from loss of cell polarity via a tumor-related inflammatory response.

The Drosophila Netrin receptor frazzled/DCC functions as an invasive tumor suppressor

BACKGROUND

Loss of heterozygosity at 18q, which includes the Deleted in Colorectal Cancer (DCC) gene, has been linked to many human cancers. However, it is unclear if loss of DCC is the specific underlying cause of these cancers. The Drosophila imaginal discs are excellent systems in which to study DCC function, as it is possible to model human tumors through the generation of somatic clones of cells bearing multiple genetic lesions. Here, these attributes of the fly system were utilized to investigate the potential tumor suppressing functions of the Drosophila DCC homologue frazzled (fra) during eye-antennal disc development.

RESULTS

Most fra loss of function clones are eliminated during development. However, when mutant clone cells generated in the developing eye were rescued from death, partially differentiated eye cells were found outside of the normal eye field, and in extreme cases distant sites of the body. Characterization of these cells during development indicates that fra mutant cells display characteristics of invasive tumor cells, including increased levels of phospho-ERK, phospho-JNK, and Mmp-1, changes in cadherin expression, remodeling of the actin cytoskeleton, and loss of polarity. Mutation of fra promotes basement membrane degradation and invasion which are repressed by inhibition of Rho1 signaling. Although inhibition of JNK signaling blocks invasive phenotypes in some metastatic cancer models in flies, blocking JNK signaling inhibits fra mutant cell death, thereby enhancing the fra mutant phenotype.

CONCLUSIONS

The results of this investigation provide the first direct link between point mutations in fra/DCC and metastatic phenotypes in an animal model and suggest that Fra functions as an invasive tumor suppressor during Drosophila development.

Cell invasion through basement membrane: the anchor cell breaches the barrier

Cell invasion through basement membrane (BM) is a specialized cellular behavior critical to many normal developmental events, immune surveillance, and cancer metastasis. A highly dynamic process, cell invasion involves a complex interplay between cell-intrinsic elements that promote the invasive phenotype, and cell-cell and cell-BM interactions that regulate the timing and targeting of BM transmigration. The intricate nature of these interactions has made it challenging to study cell invasion in vivo and model in vitro. Anchor cell invasion in Caenorhabditis elegans is emerging as an important experimental paradigm for comprehensive analysis of BM invasion, revealing the gene networks that specify invasive behavior and the interactions that occur at the cell-BM interface.

Drosophila Smt3 negatively regulates JNK signaling through sequestering Hipk in the nucleus

Post-translational modification by the small ubiquitin-related modifier (SUMO) is important for a variety of cellular and developmental processes. However, the precise mechanism(s) that connects sumoylation to specific developmental signaling pathways remains relatively less clear. Here, we show that Smt3 knockdown in Drosophila wing discs causes phenotypes resembling JNK gain of function, including ectopic apoptosis and apoptosis-induced compensatory growth. Smt3 depletion leads to an increased expression of JNK target genes Mmp1 and puckered. We show that, although knockdown of the homeodomain-interacting protein kinase (Hipk) suppresses Smt3 depletion-induced activation of JNK, Hipk overexpression synergistically enhances this type of JNK activation. We further demonstrate that Hipk is sumolylated in vivo, and its nuclear localization is dependent on the sumoylation pathway. Our results thus establish a mechanistic connection between the sumoylation pathway and the JNK pathway through the action of Hipk. We propose that the sumoylation-controlled balance between cytoplasmic and nuclear Hipk plays a crucial role in regulating JNK signaling.

Sds22/PP1 links epithelial integrity and tumor suppression via regulation of myosin II and JNK signaling

Loss of epithelial integrity often correlates with the progression of malignant tumors. Sds22, a regulatory subunit of protein phosphatase 1 (PP1), has recently been linked to regulation of epithelial polarity in Drosophila. However, its role in tumorigenesis remains obscure. In this study, using Drosophila imaginal tissue as an in vivo model system, we show that sds22 is a new potential tumor suppressor gene in Drosophila. Without sds22, cells lose epithelial architecture, and become invasive and tumorigenic when combined with Ras overexpression; conversely, sds22 overexpression can largely suppress tumorigenic growth of Ras(V12)scrib(-/-) mutant cells. Mechanistically, we show that sds22 prevents cell invasion and metastasis by inhibiting myosin II and Jun N-terminal kinase (JNK) activity downstream of PP1. Loss of this inhibition causes cells to lose epithelial organization and promotes cell invasion. Finally, human Sds22 is focally deleted and downregulated in multiple carcinomas, and this downregulation correlates with tumor progression, suggesting that sds22 inactivation may contribute to tumorigenesis and metastatic potential in human cancers via a similar mechanism.

Identification of novel Ras-cooperating oncogenes in Drosophila melanogaster: a RhoGEF/Rho-family/JNK pathway is a central driver of tumorigenesis

We have shown previously that mutations in the apico-basal cell polarity regulators cooperate with oncogenic Ras (Ras(ACT)) to promote tumorigenesis in Drosophila melanogaster and mammalian cells. To identify novel genes that cooperate with Ras(ACT) in tumorigenesis, we carried out a genome-wide screen for genes that when overexpressed throughout the developing Drosophila eye enhance Ras(ACT)-driven hyperplasia. Ras(ACT)-cooperating genes identified were Rac1 Rho1, RhoGEF2, pbl, rib, and east, which encode cell morphology regulators. In a clonal setting, which reveals genes conferring a competitive advantage over wild-type cells, only Rac1, an activated allele of Rho1 (Rho1(ACT)), RhoGEF2, and pbl cooperated with Ras(ACT), resulting in reduced differentiation and large invasive tumors. Expression of RhoGEF2 or Rac1 with Ras(ACT) upregulated Jun kinase (JNK) activity, and JNK upregulation was essential for cooperation. However, in the whole-tissue system, upregulation of JNK alone was not sufficient for cooperation with Ras(ACT), while in the clonal setting, JNK upregulation was sufficient for Ras(ACT)-mediated tumorigenesis. JNK upregulation was also sufficient to confer invasive growth of Ras(V12)-expressing mammalian MCF10A breast epithelial cells. Consistent with this, HER2(+) human breast cancers (where human epidermal growth factor 2 is overexpressed and Ras signaling upregulated) show a significant correlation with a signature representing JNK pathway activation. Moreover, our genetic analysis in Drosophila revealed that Rho1 and Rac are important for the cooperation of RhoGEF2 or Pbl overexpression and of mutants in polarity regulators, Dlg and aPKC, with Ras(ACT) in the whole-tissue context. Collectively our analysis reveals the importance of the RhoGEF/Rho-family/JNK pathway in cooperative tumorigenesis with Ras(ACT).

Regulation of Hippo signaling by Jun kinase signaling during compensatory cell proliferation and regeneration, and in neoplastic tumors

When cells undergo apoptosis, they can stimulate the proliferation of nearby cells, a process referred to as compensatory cell proliferation. The stimulation of proliferation in response to tissue damage or removal is also central to epimorphic regeneration. The Hippo signaling pathway has emerged as an important regulator of growth during normal development and oncogenesis from Drosophila to humans. Here we show that induction of apoptosis in the Drosophila wing imaginal disc stimulates activation of the Hippo pathway transcription factor Yorkie in surviving and nearby cells, and that Yorkie is required for the ability of the wing to regenerate after genetic ablation of the wing primordia. Induction of apoptosis activates Yorkie through the Jun kinase pathway, and direct activation of Jun kinase signaling also promotes Yorkie activation in the wing disc. We also show that depletion of neoplastic tumor suppressor genes, including lethal giant larvae and discs large, or activation of aPKC, activates Yorkie through Jun kinase signaling, and that Jun kinase activation is necessary, but not sufficient, for the disruption of apical-basal polarity associated with loss of lethal giant larvae. Our observations identify Jnk signaling as a modulator of Hippo pathway activity in wing imaginal discs, and implicate Yorkie activation in compensatory cell proliferation and disc regeneration.

Control of Gliotactin localization and levels by tyrosine phosphorylation and endocytosis is necessary for survival of polarized epithelia

The tricellular junction (TCJ) forms at the convergence of bicellular junctions from three adjacent cells in polarized epithelia and is necessary for maintaining the transepithelial barrier. In the fruitfly Drosophila, the TCJ is generated at the meeting point of bicellular septate junctions. Gliotactin was the first identified component of the TCJ and is necessary for TCJ and septate junction development. Gliotactin is a member of the neuroligin family and associates with the PDZ protein discs large. Beyond this interaction, little is known about the mechanisms underlying Gliotactin localization and function at the TCJ. In this study, we show that Gliotactin is phosphorylated at conserved tyrosine residues, a process necessary for endocytosis and targeting to late endosomes and lysosomes for degradation. Regulation of Gliotactin levels through phosphorylation and endocytosis is necessary as overexpression results in displacement of Gliotactin away from the TCJ throughout the septate junction domain. Excessive Gliotactin in polarized epithelia leads to delamination, paired with subsequent migration, and apoptosis. The apoptosis and the resulting compensatory proliferation resulting from high levels of Gliotactin are mediated by the Drosophila JNK pathway. Therefore, Gliotactin levels within the cell membrane are regulated to ensure correct protein localization and cell survival.

Apoptosis, stem cells, and tissue regeneration

Most metazoans have at least some ability to regenerate damaged cells and tissues, although the regenerative capacity varies depending on the species, organ, or developmental stage. Cell replacement and regeneration occur in two contexts: renewal of spent cells during tissue homeostasis (homeostatic growth), and in response to external injury, wounding, or amputation (epimorphic regeneration). Model organisms that display remarkable regenerative capacity include amphibians, planarians, Hydra, and the vertebrate liver. In addition, several mammalian organs--including the skin, gut, kidney, muscle, and even the human nervous system--have some ability to replace spent or damaged cells. Although the regenerative response is complex, it typically involves the induction of new cell proliferation through formation of a blastema, followed by cell specification, differentiation, and patterning. Stem cells and undifferentiated progenitor cells play an important role in both tissue homeostasis and tissue regeneration. Stem cells are typically quiescent or passing slowly through the cell cycle in adult tissues, but they can be activated in response to cell loss and wounding. A series of studies, mostly performed in Drosophila as well as in Hydra, Xenopus, and mouse, has revealed an unexpected role of apoptotic caspases in the production of mitogenic signals that stimulate the proliferation of stem and progenitor cells to aid in tissue regeneration. This Review summarizes some of the key findings and discusses links to stem cell biology and cancer.

The dark side of fly TNF: an ancient developmental proof reading mechanism turned into tumor promoter

The fruit fly Drosophila is an important model for biological research; however, due to its relatively short lifespan its relevance in cancer research is often questioned. Nevertheless, among many other intriguing Drosophila models, scribble group mutants provided early evidence for the existence of tumor suppressor genes and their importance in mammalian systems is beginning to emerge. In this review, I discuss recent advances in our understanding of the phenotypes of scrib group mutants, in which the activation of JNK signaling plays a crucial role. Several mechanisms can account for the activation of JNK within scrib group mutant cells, including a mechanical stress triggered by the loss of polarity, cell competition, intrinsic tumor suppression by autonomous production of Eiger, and an inflammatory response mediated by Eiger-producing haemocytes. Eiger, the sole Drosophila homolog of tumor necrosis factor, is emerging as a 'danger signal' initiated upon the presence of external pathogens, damaged tissues and the appearance of pre-malignant cells. Remarkably, in the presence of the Ras oncoprotein Eiger can act as a tumor promoter by stimulating invasive migration and delaying the onset of metamorphosis.

Oncogenic Ras diverts a host TNF tumor suppressor activity into tumor promoter

The roles of inflammatory cytokines and the immune response in cancer remain paradoxical. In the case of tumor necrosis factor (TNF), there is undisputed evidence indicating both protumor and antitumor activities. Recent work in Drosophila indicated that a TNF-dependent mechanism eliminates cells deficient for the polarity tumor suppressors dlg or scrib. In this study, however, we show that in tumors deficient for scrib that also expressed the Ras oncoprotein, the TNF signal was diverted into a protumor signal that enhanced tumor growth through larval arrest and stimulated invasive migration. In this case, TNF promoted malignancy and was detrimental to host survival. TNF was expressed at high levels by tumor-associated hemocytes recruited from the circulation. The expression of TNF by hemocytes was both necessary and sufficient to trigger TNF signaling in tumor cells. Our evidence suggests that tumors can evolve into malignancy through oncogenic Ras activation and the hijacking of TNF signaling.

A matrix metalloproteinase mediates airway remodeling in Drosophila

Organ size typically increases dramatically during juvenile growth. This growth presents a fundamental tension, as organs need resiliency to resist stresses while still maintaining plasticity to accommodate growth. The extracellular matrix (ECM) is central to providing resiliency, but how ECM is remodeled to accommodate growth is poorly understood. We investigated remodeling of Drosophila respiratory tubes (tracheae) that elongate continually during larval growth, despite being lined with a rigid cuticular ECM. Cuticle is initially deposited with a characteristic pattern of repeating ridges and valleys known as taenidia. We find that for tubes to elongate, the extracellular protease Mmp1 is required for expansion of ECM between the taenidial ridges during each intermolt period. Mmp1 protein localizes in periodically spaced puncta that are in register with the taenidial spacing. Mmp1 also degrades old cuticle at molts, promotes apical membrane expansion in larval tracheae, and promotes tube elongation in embryonic tracheae. Whereas work in other developmental systems has demonstrated that MMPs are required for axial elongation occurring in localized growth zones, this study demonstrates that MMPs can also mediate interstitial matrix remodeling during growth of an organ system.

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

In the absence of moesin, RhoA slips out of its normal role as a GTPase to activate the JNK MAPK pathway and spur apoptosis.

Precisely controlled growth and morphogenesis of developing epithelial tissues require coordination of multiple factors, including proliferation, adhesion, cell shape, and apoptosis. RhoA, a small GTPase, is known to control epithelial morphogenesis and integrity through its ability to regulate the cytoskeleton. In this study, we examine a less well-characterized RhoA function in cell survival. We demonstrate that the Drosophila melanogaster RhoA, Rho1, promotes apoptosis independently of Rho kinase through its effects on c-Jun NH₂-terminal kinase (JNK) signaling. In addition, Rho1 forms a complex with Slipper (Slpr), an upstream activator of the JNK pathway. Loss of Moesin (Moe), an upstream regulator of Rho1 activity, results in increased levels of Rho1 at the plasma membrane and cortical accumulation of Slpr. Together, these results suggest that Rho1 functions at the cell cortex to regulate JNK activity and implicate Rho1 and Moe in epithelial cell survival.

Dendrite reshaping of adult Drosophila sensory neurons requires matrix metalloproteinase-mediated modification of the basement membranes

In response to changes in the environment, dendrites from certain neurons change their shape, yet the mechanism remains largely unknown. Here we show that dendritic arbors of adult Drosophila sensory neurons are rapidly reshaped from a radial shape to a lattice-like shape within 24 hr after eclosion. This radial-to-lattice reshaping arises from rearrangement of the existing radial branches into the lattice-like pattern, rather than extensive dendrite pruning followed by regrowth of the lattice-shaped arbors over the period. We also find that the dendrite reshaping is completely blocked in mutants for the matrix metalloproteinase (Mmp) 2. Further genetic analysis indicates that Mmp2 promotes the dendrite reshaping through local degradation of the basement membrane upon which dendrites of the sensory neurons innervate. These findings suggest that regulated proteolytic alteration of the extracellular matrix microenvironment might be a fundamental mechanism to drive a large-scale change of dendritic structures during reorganization of neuronal circuits.

The Cdc42/Par6/aPKC polarity complex regulates apoptosis-induced compensatory proliferation in epithelia

BACKGROUND

In response to stress- or tissue-damage-induced apoptosis, unaffected epithelial cells undergo compensatory proliferation to maintain the integrity of the epithelium. Proximal signals regulating this response are not fully understood, but c-Jun N-terminal kinase (JNK) activity appears to be critical for both apoptosis and compensatory proliferation. Disruption of epithelial cell apical-basal polarity occurs in early cancer development and is often correlated with increased proliferation by means not fully characterized. We considered whether disruption of the various polarity complexes could provide signals identifying damaged epithelial cells and thus lead to apoptosis-induced compensatory proliferation.

RESULTS

We identify the Cdc42/Par6/atypical protein kinase C (aPKC) Par polarity complex as uniquely and specifically regulating apoptosis-induced compensatory proliferation in Drosophila epithelia. Genetic depletion of individual components or disruption of formation and localization of this complex, but not other polarity complexes, induces JNK-dependent apoptosis and JNK-dependent compensatory proliferation following radiation injury. When apoptosis execution is blocked, by p35 expression, Cdc42/Par6/aPKC-depleted tissues uniquely hyperproliferate, leading to tissue and organ overgrowth. Disruption of Cdc42/Par6/aPKC leads to activation of JNK through increased Rho1 and Rok activity and Rok's capacity to activate myosin but not F-actin.

CONCLUSIONS

We show that the Cdc42/Par6/aPKC polarity complex influences both a physiologic compensatory proliferation response after irradiation injury and a contrived compensatory non-cell-autonomous hyperproliferation response when cell-autonomous apoptosis, resulting from Cdc42/Par6/aPKC disruption, is inhibited. These results suggest the possibility that in cancer where apoptotic regulation is disrupted, loss of Cdc42/Par6/aPKC polarity complex organization or localization could contribute to tumor hyperproliferation and explain how polarity disruption contributes to tumor development.

The lethal giant larvae tumour suppressor mutation requires dMyc oncoprotein to promote clonal malignancy

Background

Neoplastic overgrowth depends on the cooperation of several mutations ultimately leading to major rearrangements in cellular behaviour. Precancerous cells are often removed by cell death from normal tissues in the early steps of the tumourigenic process, but the molecules responsible for such a fundamental safeguard process remain in part elusive. With the aim to investigate the molecular crosstalk occurring between precancerous and normal cells in vivo, we took advantage of the clonal analysis methods that are available in Drosophila for studying the phenotypes due to lethal giant larvae (lgl) neoplastic mutation induced in different backgrounds and tissues.

Results

We observed that lgl mutant cells growing in wild-type imaginal wing discs show poor viability and are eliminated by Jun N-terminal Kinase (JNK)-dependent cell death. Furthermore, they express very low levels of dMyc oncoprotein compared with those found in the surrounding normal tissue. Evidence that this is a cause of lgl mutant cells elimination was obtained by increasing dMyc levels in lgl mutant clones: their overgrowth potential was indeed re-established, with mutant cells overwhelming the neighbouring tissue and forming tumourous masses displaying several cancer hallmarks. Moreover, when lgl mutant clones were induced in backgrounds of slow-dividing cells, they upregulated dMyc, lost apical-basal cell polarity and were able to overgrow. Those phenotypes were abolished by reducing dMyc levels in the mutant clones, thereby confirming its key role in lgl-induced tumourigenesis. Furthermore, we show that the eiger-dependent Intrinsic Tumour Suppressor pathway plays only a minor role in eliminating lgl mutant cells in the wing pouch; lgl^-/- clonal death in this region is instead driven mainly by dMyc-induced Cell Competition.

Conclusions

Our results provide the first evidence that dMyc oncoprotein is required in lgl tumour suppressor mutant tissue to promote invasive overgrowth in larval and adult epithelial tissues. Moreover, we show that dMyc abundance inside versus outside the mutant clones plays a key role in driving neoplastic overgrowth.

A role for the epithelial microenvironment at tumor boundaries: evidence from Drosophila and human squamous cell carcinomas

Recent work has shown an increasing appreciation for the importance of the tumor environment, most commonly the overlying stroma. Less emphasis has been placed on the importance of local communication between transformed cells and their neighbors within the epithelium at tumor boundaries. We previously reported a Drosophila model that highlighted the importance of local interactions within the epithelial microenvironment: Src-transformed cells (Csk-deficient) were influenced by their immediate normal neighbors. The result was a consistent change in 'border cells' at the edge of transformed patches including delocalized p120-catenin and E-cadherin as well as invasive migration through the basal lamina. Here we show that the invasive properties of the boundary cells depend on up-regulation of Drosophila matrix metalloproteinase-1 as assessed by promoter activity, protein levels, in situ enzymatic activity, and tests of genetic modifier activity. Further, we provide evidence that these events at tumor borders may be evolutionarily conserved. We detected changes in 'boundary cells' within histological sections of human squamous cell carcinomas that were similar to those observed in Drosophila: both E-cadherin and p120-catenin exhibited normal junctional localization at the centers of the tumors but were reduced or delocalized at the boundary. Further, matrix metalloproteinase-2 was up regulated within these same boundary cells. These results support the view that local cell-cell interactions within the epithelial microenvironment impact tumor invasion and progression.

Spatial restriction of FGF signaling by a matrix metalloprotease controls branching morphogenesis

FGF signaling is a central regulator of branching morphogenesis processes, such as angiogenesis or the development of branched organs including lung, kidney, and mammary gland. The formation of the air sac during the development of the Drosophila tracheal system is a powerful genetic model to investigate how FGF signaling patterns such emerging structures. This article describes the characterization of the Drosophila matrix metalloprotease Mmp2 as an extracellular inhibitor of FGF morphogenetic function. Mmp2 expression in the developing air sac is controlled by the Drosophila FGF homolog Branchless and then participates in a negative feedback and lateral inhibition mechanism that defines the precise pattern of FGF signaling. The signaling function for MMPs described here may not be limited to branching morphogenesis processes.

Interaction between Ras(V12) and scribbled clones induces tumour growth and invasion

Human tumours exhibit a large degree of cellular and genetic heterogeneity 1. Complex cell interactions in the tumour and its microenvironment are thought to play a significant role in tumourigenesis and cancer progression 2. It is also known that cooperation between oncogenic genetic lesions is required for tumour development 3. However, it is not known how cell interactions contribute to oncogenic cooperation. The genetic techniques available in the fruit fly Drosophila melanogaster allow analysis of the behavior of cells with distinct mutations 4, giving this model organism a privileged position to study cell interactions and oncogenic cooperation. In Drosophila eye-antennal discs, cooperation between the oncogenic protein Ras^V125 and loss-of-function mutations in the conserved tumour suppressor scribble (scrib)6,7 gives rise to metastatic tumours that display many characteristics observed in human cancers 8-11. Here we show that clones of cells bearing different mutations can cooperate to promote tumour growth and invasion in Drosophila. We found that the Ras^V12 and scrib⁻ mutations can also cause tumours when they affect different adjacent epithelial cells. We show that this interaction between Ras^V12 and scrib⁻ clones involves JNK signaling propagation and JNK-induced upregulation of JAK/STAT-activating cytokines, a compensatory growth mechanism for tissue homeostasis. The development of Ras^V12 tumours can also be triggered by tissue damage, a stress condition that activates JNK signaling. Given the conservation of the pathways examined here, similar cooperative mechanisms could play a role in the development of human cancers.

Signal strength and signal duration define two distinct aspects of JNK-regulated axon stability

Signaling proteins often control multiple aspects of cell morphogenesis. Yet the mechanisms that govern their pleiotropic behavior are often unclear. Here we show activity levels and timing mechanisms determine distinct aspects of Jun N-terminal kinase (JNK) pathway dependent axonal morphogenesis in Drosophila mushroom body (MB) neurons. In the complete absence of Drosophila JNK (Basket), MB axons fail to stabilize, leading to their subsequent degeneration. However, with a partial loss of Basket (Bsk), or of one of the upstream JNK kinases, Hemipterous or Mkk4, these axons overextend. This suggests that Bsk activity prevents axons from destabilizing, resulting in degeneration and overextension beyond their terminal targets. These distinct phenotypes require different threshold activities involving the convergent action of two distinct JNK kinases. We show that sustained Bsk signals are essential throughout development and act additively but are dispensable at adulthood. We also suggest that graded Bsk inputs are translated into AP-1 transcriptional outputs consisting of Fos and Jun proteins.

Regulation of Drosophila matrix metalloprotease Mmp2 is essential for wing imaginal disc:trachea association and air sac tubulogenesis

The Drosophila Dorsal Air Sac Primordium (ASP) is a tracheal tube that grows toward Branchless FGF-expressing cells in the wing imaginal disc. We show that the ASP arises from a tracheal branch that invades the basal lamina of the disc to juxtapose directly with disc cells. We examined the role of matrix metalloproteases (Mmps), and found that reducing Mmp2 activity perturbed disc-trachea association, altered peritracheal distributions of collagen IV and Perlecan, misregulated ASP growth, and abrogated development of the dorsal air sacs. Whereas the function of the membrane-tethered Mmp2 in the ASP is non-cell autonomous we find that it may have distinct tissue-specific roles in the ASP and disc. These findings demonstrate a critical role for Mmp2 in tubulogenesis post-induction, and implicate Mmp2 in regulating dynamic and essential changes to the extracellular matrix.

Scribble mutants promote aPKC and JNK-dependent epithelial neoplasia independently of Crumbs

BACKGROUND

Metastatic neoplasias are characterized by excessive cell proliferation and disruptions to apico-basal cell polarity and tissue architecture. Understanding how alterations in cell polarity can impact upon tumour development is, therefore, a central issue in cancer biology. The Drosophila gene scribble (scrib) encodes a PDZ-domain scaffolding protein that regulates cell polarity and acts as a tumour suppressor in flies. Increasing evidence also implicates the loss of human Scrib in cancer. In this report, we investigate how loss of Scrib promotes epithelial tumourigenesis in Drosophila, both alone and in cooperation with oncogenic mutations.

RESULTS

We find that genetically distinct atypical protein kinase C (aPKC)-dependent and Jun N-terminal kinase (JNK)-dependent alterations in scrib mutants drive epithelial tumourigenesis. First, we show that over-expression of the apical cell polarity determinants Crumbs (Crb) or aPKC induces similar cell morphology defects and over-proliferation phenotypes as scrib loss-of-function. However, the morphological and proliferative defects in scrib mutants are independent of Crb function, and instead can be rescued by a dominant negative (kinase dead) aPKC transgene. Secondly, we demonstrate that loss of Scrib promotes oncogene-mediated transformation through both aPKC and JNK-dependent pathways. JNK normally promotes apoptosis of scrib mutant cells. However, in cooperation with oncogenic activated Ras or Notch signalling, JNK becomes an essential driver of tumour overgrowth and invasion. aPKC-dependent signalling in scrib mutants cooperates with JNK to significantly enhance oncogene-mediated tumour overgrowth.

CONCLUSION

These results demonstrate distinct aPKC and JNK-dependent pathways through which loss of Scrib promotes tumourigenesis in Drosophila. This is likely to have a direct relevance to the way in which human Scrib can similarly restrain an oncogene-mediated transformation and, more generally, on how the outcome of oncogenic signalling can be profoundly perturbed by defects in apico-basal epithelial cell polarity.

Netrin and DCC: axon guidance regulators at the intersection of nervous system development and cancer

In recent years, a number of axon guidance genes, including Netrin (Net) and Deleted in Colorectal Cancer (DCC), have been implicated in human cancers. Many of the hallmarks of human cancer, such as cell growth, invasion, evasion of apoptosis, and formation of a blood supply to the tumor, involve cellular processes that are critical during nervous system development. Here, the roles of Net-DCC in the regulation of these cellular processes in tumors and developing neurons are discussed. The advantages of using Drosophila to study the function of Net-DCC and other axon guidance molecules in these cellular processes, as well as the potential for cancer therapeutics targeting Net-DCC are highlighted.

Correcting developmental errors by apoptosis: lessons from Drosophila JNK signaling

Spatio-temporal regulation of the cell death machinery is essential for normal development and homeostasis of multicellular organisms. While the molecular basis for the central cell death machinery driven by caspases is now well documented, its regulatory mechanisms, especially in the context of living animals, remain to be clarified. The c-Jun N-terminal kinase (JNK) pathway is an evolutionarily conserved kinase cascade that regulates the apoptotic machinery. In mammals, JNK signaling has been implicated in stress-induced apoptosis. Drosophila genetics has now provided evidence of a novel role for JNK-mediated cell death signaling in eliminating developmentally aberrant cells from a tissue. The JNK-dependent cell-elimination system is orchestrated by cell-cell communication between normal and aberrant cells and is essential for ensuring developmental robustness, as well as for protecting organisms against fatal abnormalities such as neoplastic development. These processes are mediated by cell competition, morphogenetic apoptosis, and intrinsic tumor suppression. A combinatorial approach using both genetic and live-imaging systems in Drosophila will be extremely powerful to decipher how JNK-mediated apoptosis works within multicellular communities.

At the crossroads of polarity, proliferation and apoptosis: the use of Drosophila to unravel the multifaceted role of endocytosis in tumor suppression

Endocytosis is an important regulator of cell-cell signaling and endocytic trafficking has been increasingly implicated in control of tumor suppression. Recent insights from Drosophila indicate that impairment of multiple trafficking steps which lead to receptor degradation can cause tumor formation in epithelial organs. These tumors are characterized by sustained activation of a number of mitogenic signaling pathways, and by subversion of epithelial polarity and the apoptotic response. Cooperation between such alterations, as well as tumor-host interactions, is also observed. The recapitulation of several hallmarks of human cancers in fly tumors provides a framework to understand the role of defective endocytosis in cancer.

A drosophila model for EGFR-Ras and PI3K-dependent human glioma

Gliomas, the most common malignant tumors of the nervous system, frequently harbor mutations that activate the epidermal growth factor receptor (EGFR) and phosphatidylinositol-3 kinase (PI3K) signaling pathways. To investigate the genetic basis of this disease, we developed a glioma model in Drosophila. We found that constitutive coactivation of EGFR-Ras and PI3K pathways in Drosophila glia and glial precursors gives rise to neoplastic, invasive glial cells that create transplantable tumor-like growths, mimicking human glioma. Our model represents a robust organotypic and cell-type-specific Drosophila cancer model in which malignant cells are created by mutations in signature genes and pathways thought to be driving forces in a homologous human cancer. Genetic analyses demonstrated that EGFR and PI3K initiate malignant neoplastic transformation via a combinatorial genetic network composed primarily of other pathways commonly mutated or activated in human glioma, including the Tor, Myc, G1 Cyclins-Cdks, and Rb-E2F pathways. This network acts synergistically to coordinately stimulate cell cycle entry and progression, protein translation, and inappropriate cellular growth and migration. In particular, we found that the fly orthologs of CyclinE, Cdc25, and Myc are key rate-limiting genes required for glial neoplasia. Moreover, orthologs of Sin1, Rictor, and Cdk4 are genes required only for abnormal neoplastic glial proliferation but not for glial development. These and other genes within this network may represent important therapeutic targets in human glioma.

Malignant gliomas, tumors composed of glial cells and their precursors, are the most common and deadly human brain tumors. These tumors infiltrate the brain and proliferate rapidly, properties that render them largely incurable even with current therapies. Mutations in genes within the EGFR-Ras and PI3K signaling pathways are common in malignant gliomas, although how these genes specifically control glial pathogenesis is unclear. To investigate the genetic basis of this disease, we developed a glioma model in the fruit fly, Drosophila melanogaster. We found that constitutive coactivation of the EGFR-Ras and PI3K pathways in Drosophila glia gives rise to highly proliferative and invasive neoplastic cells that create transplantable tumor-like growths, mimicking human glioma. This represents a robust cell-type-specific Drosophila cancer model in which malignant cells are created by mutations in genetic pathways thought to be driving forces in a homologous human cancer. Genetic analyses demonstrated that EGFR-Ras and PI3K induce fly glial neoplasia through activation of a combinatorial genetic network composed, in part, of other genetic pathways also commonly mutated in human glioma. This network acts synergistically to coordinately stimulate cellular proliferation, protein translation, and inappropriate migration. Rate-limiting genes within this network may represent important therapeutic targets in human glioma.

Distinct functions for the catalytic and hemopexin domains of a Drosophila matrix metalloproteinase

Human matrix metalloproteinases (MMPs) are believed to contribute to tumor progression. Therapies based on inhibiting the catalytic domain of MMPs have been unsuccessful, but these studies raise the question of whether other MMP domains might be appropriate targets. The genetic dissection of domain function has been stymied in mouse because there are 24 related and partially redundant MMP genes in the mouse genome. Here, we present a genetic dissection of the functions of the hemopexin and catalytic domains of a canonical MMP in Drosophila melanogaster, an organism with only 2 MMPs that function nonredundantly. We compare the phenotypes of Mmp1 null alleles with alleles that have specific hemopexin domain lesions, and we also examine phenotypes of dominant-negative mutants. We find that, although the catalytic domain appears to be required for all MMP functions including extracellular matrix remodeling of the tracheal system, the hemopexin domain is required specifically for tissue invasion events later in metamorphosis but not for tracheal remodeling. Thus, we find that this MMP hemopexin domain has an apparent specialization for tissue invasion events, a finding with potential implications for inhibitor therapies.

Drosophila melanogaster as a model organism of brain diseases

Drosophila melanogaster has been utilized to model human brain diseases. In most of these invertebrate transgenic models, some aspects of human disease are reproduced. Although investigation of rodent models has been of significant impact, invertebrate models offer a wide variety of experimental tools that can potentially address some of the outstanding questions underlying neurological disease. This review considers what has been gleaned from invertebrate models of neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, metabolic diseases such as Leigh disease, Niemann-Pick disease and ceroid lipofuscinoses, tumor syndromes such as neurofibromatosis and tuberous sclerosis, epilepsy as well as CNS injury. It is to be expected that genetic tools in Drosophila will reveal new pathways and interactions, which hopefully will result in molecular based therapy approaches.

Control of tumourigenesis by the Scribble/Dlg/Lgl polarity module

The neoplastic tumour suppressors, Scribble, Dlg and Lgl, originally discovered in the vinegar fly Drosophila melanogaster, are currently being actively studied for their potential role in mammalian tumourigenesis. In Drosophila, these tumour suppressors function in a common genetic pathway to regulate apicobasal cell polarity and also play important roles in the control of cell proliferation, survival, differentiation and in cell migration/invasion. The precise mechanism by which Scribble, Dlg and Lgl function is not clear; however, they have been implicated in the regulation of signalling pathways, vesicle trafficking and in the Myosin II-actin cytoskeleton. We review the evidence for the involvement of Scribble, Dlg, and Lgl in cancer, and how the various functions ascribed to these tumour suppressors in Drosophila and mammalian systems may impact on the process of tumourigenesis.

Phosphorylation networks regulating JNK activity in diverse genetic backgrounds

Cellular signaling networks have evolved to enable swift and accurate responses, even in the face of genetic or environmental perturbation. Thus, genetic screens may not identify all the genes that regulate different biological processes. Moreover, although classical screening approaches have succeeded in providing parts lists of the essential components of signaling networks, they typically do not provide much insight into the hierarchical and functional relations that exist among these components. We describe a high-throughput screen in which we used RNA interference to systematically inhibit two genes simultaneously in 17,724 combinations to identify regulators of Drosophila JUN NH(2)-terminal kinase (JNK). Using both genetic and phosphoproteomics data, we then implemented an integrative network algorithm to construct a JNK phosphorylation network, which provides structural and mechanistic insights into the systems architecture of JNK signaling.

Normal dendrite growth in Drosophila motor neurons requires the AP-1 transcription factor

During learning and memory formation, information flow through networks is regulated significantly through structural alterations in neurons. Dendrites, sites of signal integration, are key targets of activity-mediated modifications. Although local mechanisms of dendritic growth ensure synapse-specific changes, global mechanisms linking neural activity to nuclear gene expression may have profound influences on neural function. Fos, being an immediate-early gene, is ideally suited to be an initial transducer of neural activity, but a precise role for the AP-1 transcription factor in dendrite growth remains to be elucidated. Here we measure changes in the dendritic fields of identified Drosophila motor neurons in vivo and in primary culture to investigate the role of the immediate-early transcription factor AP-1 in regulating endogenous and activity-induced dendrite growth. Our data indicate that (a) increased neural excitability or depolarization stimulates dendrite growth, (b) AP-1 (a Fos, Jun hetero-dimer) is required for normal motor neuron dendritic growth during development and in response to activity induction, and (c) neuronal Fos protein levels are rapidly but transiently induced in motor neurons following neural activity. Taken together, these results show that AP-1 mediated transcription is important for dendrite growth, and that neural activity influences global dendritic growth through a gene-expression dependent mechanism gated by AP-1.

An innate immune response of blood cells to tumors and tissue damage in Drosophila

Studies in mice and humans have demonstrated a role for the immune system in preventing the growth of tumors. Deciphering the mechanisms involved in the immune response to tumors is essential to our understanding of immune recognition and cancer progression. Here we report an innate immune response to tumors in Drosophila melanogaster. We found that circulating blood cells, termed hemocytes, adhere to tumors upon detection of basement membrane disruption, and subsequently counter their growth. Basement membrane components are remarkably conserved throughout the animal kingdom, providing a unique structure for the immune system to sense tissue integrity. Further, we show that tissue damage activates JNK signaling in both tumors and aseptic wounds, causing expression of JAK/STAT-activating cytokines. Cytokine secretion from the injured tissue is amplified into a systemic response through the induction of additional cytokine expression in the hemocytes and the fat body, resulting in hemocyte proliferation. Our findings reveal common mechanisms in the response to tumors and wounds in flies. A similar innate reaction may underlie the response to tumors and tissue damage in vertebrates and humans.

Regulation of early endosomal entry by the Drosophila tumor suppressors Rabenosyn and Vps45

The small GTPase Rab5 has emerged as an important regulator of animal development, and it is essential for endocytic trafficking. However, the mechanisms that link Rab5 activation to cargo entry into early endosomes remain unclear. We show here that Drosophila Rabenosyn (Rbsn) is a Rab5 effector that bridges an interaction between Rab5 and the Sec1/Munc18-family protein Vps45, and we further identify the syntaxin Avalanche (Avl) as a target for Vps45 activity. Rbsn and Vps45, like Avl and Rab5, are specifically localized to early endosomes and are required for endocytosis. Ultrastructural analysis of rbsn, Vps45, avl, and Rab5 null mutant cells, which show identical defects, demonstrates that all four proteins are required for vesicle fusion to form early endosomes. These defects lead to loss of epithelial polarity in mutant tissues, which overproliferate to form neoplastic tumors. This work represents the first characterization of a Rab5 effector as a tumor suppressor, and it provides in vivo evidence for a Rbsn-Vps45 complex on early endosomes that links Rab5 to the SNARE fusion machinery.

Remodeling the model organism: matrix metalloproteinase functions in invertebrates

The matrix metalloproteinase (MMP) family of extracellular proteases is conserved throughout the animal kingdom. Studies of invertebrate MMPs have demonstrated they are involved in tissue remodeling. In Drosophila, MMPs are required for histolysis, tracheal growth, tissue invasion, axon guidance, and dendritic remodeling. Recent work demonstrates that MMPs also participate in Drosophila tumor invasion. In Caenorhabditis elegans an MMP is involved in anchor cell invasion; a Hydra MMP is important for regeneration and maintaining cell identity; and a sea urchin MMP degrades matrix to allow hatching. In worms and in flies, MMPs are regulated by the JNK pathway.