Epithelial monitoring through ligand-receptor segregation ensures malignant cell elimination

Epithelial cell competition is promoted by signaling from immune cells

In epithelial tissues, juxtaposition of cells of different phenotypes can trigger cell competition, a process whereby one type of cell drives death and extrusion of another. During growth and homeostasis, cell competition is thought to serve a quality control function, eliminating cells that are "less fit". Tissues may also attack and eliminate newly arising tumor cells, exploiting mechanisms shared with other instances of cell competition, but that differ, reportedly, in the involvement of the immune system. Whereas immune cells have been shown to play a direct role in killing tumor cells, this has not been observed in other cases of cell competition, suggesting that tissues recognize and handle cancer cells differently. Here, we challenge this view, showing that, in the fruit fly Drosophila, innate immune cells play similar roles in cell killing during classical cell competition as in eliminating tumors. These findings suggest that immune suppression of cancer may exploit the same mechanisms as are involved in promoting phenotypic uniformity among epithelial cells.

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.

In vivo measurements of receptor tyrosine kinase activity reveal feedback regulation of a developmental gradient

A lack of tools for detecting receptor activity in vivo has limited our ability to fully explore receptor-level control of developmental patterning. Here, we extend a new class of biosensors for receptor tyrosine kinase (RTK) activity, the pYtag system, to visualize endogenous RTK activity in Drosophila. We build biosensors for three Drosophila RTKs that function across developmental stages and tissues. By characterizing Torso::pYtag during terminal patterning in the early embryo, we find that Torso activity differs from downstream ERK activity in two surprising ways: Torso activity is narrowly restricted to the poles but produces a broader gradient of ERK, and Torso activity decreases over developmental time while ERK activity is sustained. This decrease in Torso activity is driven by ERK pathway-dependent negative feedback. Our results suggest an updated model of terminal patterning where a narrow domain of Torso activity, tuned in amplitude by negative feedback, locally activates signaling effectors which diffuse through the syncytial embryo to form the ERK gradient. Altogether, this work highlights the usefulness of pYtags for investigating receptor-level regulation of developmental patterning.

Design of aggregation-induced emission materials for biosensing of molecules and cells

In recent years, aggregation-induced emission (AIE) materials have gained significant attention and have been developed for various applications in different fields including biomedical research, chemical analysis, optoelectronic devices, materials science, and nanotechnology. AIE is a unique luminescence phenomenon, and AIEgens are fluorescent moieties with relatively twisted structures that can overcome the aggregation-caused quenching (ACQ) effect. Additionally, AIEgens offer advantages such as non-washing properties, deep tissue penetration, minimal damage to biological structures, high signal-to-noise ratio, and excellent photostability. Fluorescent probes with AIE characteristics exhibit high sensitivity, short response time, simple operation, real-time detection capability, high selectivity, and excellent biocompatibility. As a result, they have been widely applied in cellular imaging, luminescent sensing, detection of physiological abnormalities in the human body, as well as early diagnosis and treatment of diseases. This review provides a comprehensive summary and discussion of the progress over the past four years regarding the detection of metal ions, small chemical molecules, biomacromolecules, microbes, and cells based on AIE materials, along with discussing their potential applications and future development prospects.

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.

Sex-dimorphic tumor growth is regulated by tumor microenvironmental and systemic signals

Tumor growth and progression involve coordinated regulation by internal, microenvironmental, and systemic signals and often display conspicuous sexual dimorphism. The mechanisms governing the integration and coordination of these signals, along with their sex-based differences, remain largely unknown. Using a Drosophila tumor model originating from nonreproductive tissue, we show that female-biased tumor growth involves multifaceted communications among tumor cells, hemocytes, and neuroendocrine insulin-producing cells (IPCs). Notch-active tumor cells recruit hemocytes carrying the tumor necrosis factor-α (TNF-α) homolog Eiger to the tumor microenvironment (TME), activating the c-Jun N-terminal kinase (JNK) pathway in tumor cells, instigating the sexually dimorphic up-regulation of cytokine Unpaired 2 (Upd2). Upd2, in turn, exerts a distal influence by modulating the release of a Drosophila insulin-like peptide (Dilp2) from IPCs. Dilp2 then activates the insulin signaling in the tumor, thereby fostering sexual-dimorphic tumor growth. Together, these findings reveal a relay mechanism involving the TME and systemic signals that collectively control the sexual dimorphism of tumor growth.

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.

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 over-proliferate, 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.

The JNK and Hippo pathways control epithelial integrity and prevent tumor initiation by regulating an overlapping transcriptome

Epithelial organs maintain their integrity and prevent tumor initiation by actively removing defective cells, such as those that have lost apicobasal polarity. Here, we identify how transcription factors of two key signaling pathways-Jun-N-terminal kinase (JNK) and Hippo-regulate epithelial integrity by controlling transcription of an overlapping set of target genes. Targeted DamID experiments reveal that, in proliferating cells of the Drosophila melanogaster eye, the AP-1 transcription factor Jun and the Hippo pathway transcription regulators Yorkie and Scalloped bind to a common suite of target genes that promote organ growth. In defective neoplastic cells, AP-1 transcription factors repress transcription of growth genes together with the C-terminal binding protein (CtBP) co-repressor. If gene repression by AP-1/CtBP fails, neoplastic tumor growth ensues, driven by Yorkie/Scalloped. Thus, AP-1/CtBP eliminates defective cells and prevents tumor initiation by acting in parallel to Yorkie/Scalloped to repress expression of a shared transcriptome. These findings shed new light on the maintenance of epithelial integrity and tumor suppression.

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.

Damage control of epithelial barrier function in dynamic environments

Epithelial tissues cover the surfaces and lumens of the internal organs of multicellular animals and crucially contribute to internal environment homeostasis by delineating distinct compartments within the body. This vital role is known as epithelial barrier function. Epithelial cells are arranged like cobblestones and intricately bind together to form an epithelial sheet that upholds this barrier function. Central to the restriction of solute and fluid diffusion through intercellular spaces are occluding junctions, tight junctions in vertebrates and septate junctions in invertebrates. As part of epithelial tissues, cells undergo constant renewal, with older cells being replaced by new ones. Simultaneously, the epithelial tissue undergoes relative rearrangement, elongating, and shifting directionally as a whole. The movement or shape changes within the epithelial sheet necessitate significant deformation and reconnection of occluding junctions. Recent advancements have shed light on the intricate mechanisms through which epithelial cells sustain their barrier function in dynamic environments. This review aims to introduce these noteworthy findings and discuss some of the questions that remain unanswered.

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.

Toward a predictive understanding of epithelial cell death

Epithelial cell death is highly prevalent during development and tissue homeostasis. While we have a rather good understanding of the molecular regulators of programmed cell death, especially for apoptosis, we still fail to predict when, where, how many and which specific cells will die in a tissue. This likely relies on the much more complex picture of apoptosis regulation in a tissular and epithelial context, which entails cell autonomous but also non-cell autonomous factors, diverse feedback and multiple layers of regulation of the commitment to apoptosis. In this review, we illustrate this complexity of epithelial apoptosis regulation by describing these different layers of control, all demonstrating that local cell death probability is a complex emerging feature. We first focus on non-cell autonomous factors that can locally modulate the rate of cell death, including cell competition, mechanical input and geometry as well as systemic effects. We then describe the multiple feedback mechanisms generated by cell death itself. We also outline the multiple layers of regulation of epithelial cell death, including the coordination of extrusion and regulation occurring downstream of effector caspases. Eventually, we propose a roadmap to reach a more predictive understanding of cell death regulation in an epithelial context.

Automated counting of Drosophila imaginal disc cell nuclei

Automated image quantification workflows have dramatically improved over the past decade, enriching image analysis and enhancing the ability to achieve statistical power. These analyses have proved especially useful for studies in organisms such as Drosophila melanogaster, where it is relatively simple to obtain high sample numbers for downstream analyses. However, the developing wing, an intensively utilized structure in developmental biology, has eluded efficient cell counting workflows due to its highly dense cellular population. Here, we present efficient automated cell counting workflows capable of quantifying cells in the developing wing. Our workflows can count the total number of cells or count cells in clones labeled with a fluorescent nuclear marker in imaginal discs. Moreover, by training a machine-learning algorithm we have developed a workflow capable of segmenting and counting twin-spot labeled nuclei, a challenging problem requiring distinguishing heterozygous and homozygous cells in a background of regionally varying intensity. Our workflows could potentially be applied to any tissue with high cellular density, as they are structure-agnostic, and only require a nuclear label to segment and count cells.

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.

Diamond controls epithelial polarity through the dynactin-dynein complex

Epithelial polarity is critical for proper functions of epithelial tissues, tumorigenesis, and metastasis. The evolutionarily conserved transmembrane protein Crumbs (Crb) is a key regulator of epithelial polarity. Both Crb protein and its transcripts are apically localized in epithelial cells. However, it remains not fully understood how they are targeted to the apical domain. Here, using Drosophila ovarian follicular epithelia as a model, we show that epithelial polarity is lost and Crb protein is absent in the apical domain in follicular cells (FCs) in the absence of Diamond (Dind). Interestingly, Dind is found to associate with different components of the dynactin-dynein complex through co-IP-MS analysis. Dind stabilizes dynactin and depletion of dynactin results in almost identical defects as those observed in dind-defective FCs. Finally, both Dind and dynactin are also required for the apical localization of crb transcripts in FCs. Thus our data illustrate that Dind functions through dynactin/dynein-mediated transport of both Crb protein and its transcripts to the apical domain to control epithelial apico-basal (A/B) polarity.

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.

Drosophila TNF/TNFRs: At the crossroad between metabolism, immunity, and tissue homeostasis

Tumor necrosis factor (TNF)-α is a highly conserved proinflammatory cytokine with important functions in immunity, tissue repair, and cellular homeostasis. Due to the simplicity of the Drosophila TNF-TNF receptor (TNFR) system and a broad genetic toolbox, the fly has played a pivotal role in deciphering the mechanisms underlying TNF-mediated physiological and pathological functions. In this review, we summarize the recent advances in our understanding of how local and systemic sources of Egr/TNF contribute to its antitumor and tumor-promoting properties, and its emerging functions in adaptive growth responses, sleep regulation, and adult tissue homeostasis. The recent annotation of TNF as an adipokine and its indisputable contribution to obesity- and cancer-associated metabolic diseases have provoked a new area of research focusing on its dual function in regulating immunity and energy homeostasis. Here, we discuss the role of TNFR signaling in coupling immune and metabolic processes and how this might be relevant in the adaption of host to environmental stresses, or, in the case of obesity, promote metabolic derangements and disease.

The cell adhesion molecule Echinoid promotes tissue survival and separately restricts tissue overgrowth in Drosophila imaginal discs

The interactions that cells in Drosophila imaginal discs have with their neighbors are known to regulate their ability to survive. In a screen of genes encoding cell surface proteins for gene knockdowns that affect the size or shape of mutant clones, we found that clones of cells with reduced levels of echinoid (ed) are fewer, smaller, and can be eliminated during development. In contrast, discs composed mostly of ed mutant tissue are overgrown. We find that ed mutant tissue has lower levels of the anti-apoptotic protein Diap1 and has increased levels of apoptosis which is consistent with the observed underrepresentation of ed mutant clones and the slow growth of ed mutant tissue. The eventual overgrowth of ed mutant tissue results not from accelerated growth, but from prolonged growth resulting from a failure to arrest growth at the appropriate final size. Ed has previously been shown to physically interact with multiple Hippo-pathway components and it has been proposed to promote Hippo pathway signaling, to exclude Yorkie (Yki) from the nucleus, and restrain the expression of Yki-target genes. We did not observe changes in Yki localization in ed mutant tissue and found decreased levels of expression of several Yorkie-target genes, findings inconsistent with the proposed effect of Ed on Yki. We did, however, observe increased expression of several Yki-target genes in wild-type cells neighboring ed mutant cells, which may contribute to elimination of ed mutant clones. Thus, ed has two distinct functions: an anti-apoptotic function by maintaining Diap1 levels, and a function to arrest growth at the appropriate final size. Both of these are unlikely to be explained by a simple effect on the Hippo pathway.

Ribosomal protein mutations and cell competition: autonomous and nonautonomous effects on a stress response

Ribosomal proteins (Rps) are essential for viability. Genetic mutations affecting Rp genes were first discovered in Drosophila, where they represent a major class of haploinsufficient mutations. One mutant copy gives rise to the dominant "Minute" phenotype, characterized by slow growth and small, thin bristles. Wild-type (WT) and Minute cells compete in mosaics, that is, Rp+/- are preferentially lost when their neighbors are of the wild-type genotype. Many features of Rp gene haploinsufficiency (i.e. Rp+/- phenotypes) are mediated by a transcriptional program. In Drosophila, reduced translation and slow growth are under the control of Xrp1, a bZip-domain transcription factor induced in Rp mutant cells that leads ultimately to the phosphorylation of eIF2α and consequently inhibition of most translation. Rp mutant phenotypes are also mediated transcriptionally in yeast and in mammals. In mammals, the Impaired Ribosome Biogenesis Checkpoint activates p53. Recent findings link Rp mutant phenotypes to other cellular stresses, including the DNA damage response and endoplasmic reticulum stress. We suggest that cell competition results from nonautonomous inputs to stress responses, bringing decisions between adaptive and apoptotic outcomes under the influence of nearby cells. In Drosophila, cell competition eliminates aneuploid cells in which loss of chromosome leads to Rp gene haploinsufficiency. The effects of Rp gene mutations on the whole organism, in Minute flies or in humans with Diamond-Blackfan Anemia, may be inevitable consequences of pathways that are useful in eliminating individual cells from mosaics. Alternatively, apparently deleterious whole organism phenotypes might be adaptive, preventing even more detrimental outcomes. In mammals, for example, p53 activation appears to suppress oncogenic effects of Rp gene haploinsufficiency.

Automated counting of Drosophila imaginal disc cell nuclei

Automated image quantification workflows have dramatically improved over the past decade, enriching image analysis and enhancing the ability to achieve statistical power. These analyses have proved especially useful for studies in organisms such as Drosophila melanogaster, where it is relatively simple to obtain high sample numbers for downstream analyses. However, the developing wing, an intensively utilized structure in developmental biology, has eluded efficient cell counting workflows due to its highly dense cellular population. Here, we present efficient automated cell counting workflows capable of quantifying cells in the developing wing. Our workflows can count the total number of cells or count cells in clones labeled with a fluorescent nuclear marker in imaginal discs. Moreover, by training a machine-learning algorithm we have developed a workflow capable of segmenting and counting twin-spot labeled nuclei, a challenging problem requiring distinguishing heterozygous and homozygous cells in a background of regionally varying intensity. Our workflows could potentially be applied to any tissue with high cellular density, as they are structure-agnostic, and only require a nuclear label to segment and count cells.

Exploiting the Receptor-Binding Domains of R-Spondin 1 to Target Leucine-Rich Repeat-Containin G-Coupled Protein Receptor 5-Expressing Stem Cells in Ovarian Cancer

Leucine-rich repeat-containing G-protein-coupled receptor (LGR5) and LGR6 mark epithelial stem cells in normal tissues and tumors. They are expressed by stem cells in the ovarian surface and fallopian tube epithelia from which ovarian cancer arises. High-grade serous ovarian cancer is unique in expressing unusually high levels of LGR5 and LGR6 mRNA. R-spondins are the natural ligands for LGR5 and LGR6 to which they bind with nanomolar affinity. To target stem cells in ovarian cancer, we used the sortase reaction to site-specifically conjugate the potent cytotoxin monomethyl auristatin E (MMAE) via a protease sensitive linker to the two furin-like domains of RSPO1 (Fu1-Fu2) that mediate its binding to LGR5 and LGR6 and their co-receptors Zinc And Ring Finger 3 and Ring Finger Protein 43 via a protease-cleavable linker. An immunoglobulin Fc domain added to the N-terminal end served to dimerize the receptor-binding domains so that each molecule carries two MMAE. The resulting molecule, FcF2-MMAE, demonstrated: 1) selective LGR5-dependent low nanomolar cytotoxicity against ovarian cancer cells in vitro; 2) selectivity that was dependent on binding to both the LGR receptors and ubiquitin ligase co-receptors; 3) favorable stability and plasma pharmacokinetic properties when administered intravenously with an elimination half-life of 29.7 hours; 4) selective inhibition of LGR5-rich as opposed to isogenic LGR5-poor tumors in vivo; and, 5) therapeutic efficacy in three aggressive wild-type human ovarian cancer xenograft models. These results demonstrate the successful use of the Fu1-Fu2 domain of RSPO1 as a drug carrier and the ability of FcF2-MMAE to target cells in tumors that express stem cell markers. SIGNIFICANCE STATEMENT: FcF2-MMAE is a novel cancer therapeutic that exploits the high-affinity binding domains of RSPO1 to target monomethyl auristatin E to tumor stem cells that express LGR5. FcF2-MMAE has low nanomolar LGR5-dependent cytotoxicity in vitro, favorable pharmacokinetics, and differential efficacy in an isogenic LGR5-poor versus LGR5-rich ovarian cancer xenograft model when given on a weekly schedule.

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.

PTP10D-mediated cell competition is not obligately required for elimination of polarity-deficient clones

Animal organs maintain tissue integrity and ensure removal of aberrant cells through several types of surveillance mechanisms. One prominent example is the elimination of polarity-deficient mutant cells within developing Drosophila imaginal discs. This has been proposed to require heterotypic cell competition dependent on the receptor tyrosine phosphatase PTP10D within the mutant cells. We report here experiments to test this requirement in various contexts and find that PTP10D is not obligately required for the removal of scribble (scrib) mutant and similar polarity-deficient cells. Our experiments used identical stocks with which another group can detect the PTP10D requirement, and our results do not vary under several husbandry conditions including high and low protein food diets. Although we are unable to identify the source of the discrepant results, we suggest that the role of PTP10D in polarity-deficient cell elimination may not be absolute.