Biology subjects

Zimmermann, M.

Publications and source records attributed to Zimmermann, M..

At least 37 records · Page 2Linked to original sources

bioRxiv2025

Targeting CXADR-mediated AKT signaling suppresses tumorigenesis and enhances chemotherapy efficacy in Ewing sarcoma

Distant metastasis is the leading cause of mortality in Ewing sarcoma (EwS) - a malignant bone or soft-tissue cancer mainly affecting children, adolescents, and young adults. Despite continuous efforts in understanding its pathogenesis, the molecular mechanisms driving EwS metastasis remain poorly understood, thus limiting the potential for therapeutic progress. Here, we identify the tight junction component Coxsackievirus and Adenovirus receptor (CXADR) as a critical regulator of cancer progression and metastasis in EwS. Differential gene expression analysis of patient tumors from two independent cohorts revealed that elevated CXADR levels are associated with metastatic disease and poor overall survival. In functional experiments, conditional CXADR knockdown reduced the growth of EwS cell line models in vitro, and suppressed local tumorigenesis. Notably, CXADR knockdown completely abrogated metastasis formation in vivo. Integration of transcriptome profiling and mechanistic studies uncovered that CXADR promotes the activation of AKT signaling, likely through complex formation with PTEN. Consequently, pharmacological targeting of AKT using the FDA-approved pan-AKT inhibitor Capivasertib showed CXADR-dependent cytotoxicity, with enhanced efficacy if combined with the EwS standard-of-care chemotherapeutic agent Vincristine. Collectively, our findings establish CXADR as a prognostic and predictive biomarker in EwS, highlighting AKT inhibition combined with chemotherapy as a promising strategy for patients with high CXADR expression. Together, these findings support a precision medicine approach combining molecular stratification and targeted therapies to improve patient outcomes in metastatic EwS.

cancer biology↗

bioRxiv2025

cIAP1 inhibitor of apoptosis is a tumor suppressor in Ewing sarcoma

Ewing sarcoma (EwS) is a highly aggressive pediatric malignancy driven by EWSR1::ETS fusion oncoproteins -primarily EWSR1::FLI1- which deregulate genes essential for differentiation, proliferation, and cell survival. To uncover key downstream targets of this fusion involved in cell differentiation, we combined transcriptomic profiling of EwS cell lines following EWSR1::FLI1 inhibition with gene ontology analysis, a clinically annotated gene expression dataset derived from EwS patient material and network analyses. This integrative approach identified inhibitor of apoptosis protein 1 (cIAP1, alias BIRC2) as an EWSR1::FLI1-suppresed gene. Despite its known oncogenic role in many cancers, cIAP1 showed minimal expression in EwS. Using inducible cIAP1 re-expression models in EwS cells, we demonstrated that cIAP1 re-expression suppresses proliferation, clonogenic growth, and 3D spheroid formation in vitro. Transcriptomic and proteomic analyses revealed that low cIAP1 expression enhances proliferation-related gene signatures, which are inhibited upon cIAP1 re-expression. In vivo xenograft models revealed that cIAP1 re-expression significantly reduces tumor growth, mitotic activity, and Ki-67 positivity, while increasing tumor necrosis and apoptosis. These findings highlight an unexpected tumor-suppressive role for cIAP1 in fusion-driven sarcomas, contrasting with its pro-survival function in other cancers. Collectively, our results identify cIAP1 as a prognostically relevant, EWSR1::FLI1-regulated hub whose re-expression disrupts tumor progression, offering a potential therapeutic strategy to restore tumor-suppressive pathways in EwS.

cancer biology↗

bioRxiv2025

Cell-type specific iron content regulation revealed by single-cell iron quantification

Iron is crucial for cellular metabolism and cell growth. Nevertheless, in humans, both iron deficiency and disorders of iron overload are widespread. How cellular iron content varies depending upon iron availability, and how this influences cell function is poorly characterised. We developed a method to quantify metals in hundreds of cells per minute via single-cell inductively-coupled plasma mass spectrometry (sc-ICP-MS), and used this to explore iron usage by immune cells. Activated murine T-cells exposed to a 625-fold titration of extracellular iron maintained close homeostatic control, with iron content varying by [~]20%. However, these variations strongly correlated with activation characteristics and proliferation. Running sc-ICP-MS downstream of flow cytometric sorting showed that murine T-cells and B-cells ex vivo exhibit similar mean and heterogeneity of cellular iron while splenic macrophages contain twice as much iron and more heterogeneous iron content. Finally, activated human B-cells contain [~]10-fold more iron per cell than murine B-cells. We suggest that mechanisms of iron homeostasis impart particular ranges or set-points of iron content to different cell types and activation states, and that small changes in iron content have large effects on cell behaviour. Our methodological advance and consequent findings suggest new approaches to studying the biology of metals.

cell biology↗

bioRxiv2025

Establishing an in vitro pipeline for the high-throughput quantification of epithelial permeability of gut bacterial metabolites

The epithelium of the human gastrointestinal tract is key for controlling the absorption of small molecules and for forming a tight barrier between the gut microbiota and the host, thereby maintaining metabolic homeostasis. Both the microbiota and the barrier function of the intestinal epithelium have a role in pharmacokinetic variability of medical drugs. In this study, we developed a high-throughput workflow to assess the absorption of bacterially produced (drug) metabolites by intestinal epithelial cells through the combination of anaerobic bacterial cultures and human-intestine derived Caco2 cell cultures in a transwell system. To functionally monitor the barrier integrity during the experiments, we introduced a panel of marker compounds, whose concentration kinetics on either side of the epithelial monolayer indicates barrier integrity and transport. We employed this workflow to systematically probe the effect of different gut bacterial species on the epithelial absorption of 482 drugs and their 172 bacterially produced metabolites. While we could recapitulate known bacterial drug biotransformation reactions and expected drug metabolite absorption profiles, we also identified 33 new bacteria-drug pairs for which bacterial biotransformation alters epithelial permeability. Further, we combined the developed experimental workflow with untargeted metabolomics analysis to systematically study epithelial permeability of metabolites naturally produced by gut bacteria. Tracking the absorption kinetics of 397 bacterially produced metabolites revealed that the majority (>79%) of these metabolites do not pass the Caco2 monolayer, illustrating its role as a physical and metabolic barrier. In summary, we present a highly adaptable high-throughput workflow to quantitatively study the metabolic interactions at the intestinal microbiota-host interface which can impact pharmacokinetics, toxicokinetics, and human physiology.

pharmacology and toxicology↗

bioRxiv2025

EWSR1::ETS-low cells promote metabolic reprogramming of the tryptophan-kynurenine-AHR axis, immunosuppression, and poor outcome in Ewing sarcoma

The extent to which dynamic changes in oncogene activity shape cancer cell metabolism and drive disease progression remains poorly understood. Ewing sarcoma (EwS), driven by EWSR1::ETS fusion transcription factors, constitutes an ideal model to interrogate this question, as fluctuations in fusion activity direct divergent transcriptional programs. While EWSR1::ETS-high cells display a rather sessile but proliferative phenotype, EWSR1::ETS-low cells are more invasive. Yet, the mechanisms underlying these different phenotypes remain poorly characterized. Here, by employing an integrative functional metabolomics approach, we link reduced EWSR1::ETS activity in primary EwS tumors to adverse clinical outcome and pronounced activation of the aryl hydrocarbon receptor (AHR) pathway. Low EWSR1::ETS states foster tryptophan catabolism and accumulation of the AHR agonist kynurenine, which in turn promotes an immunosuppressive tumor microenvironment characterized by impaired natural killer (NK) cell cytotoxicity and enrichment of immunoregulatory infiltrates. Functionally, AHR silencing restores NK cell-mediated tumor recognition, while also directly suppressing EwS cell proliferation, clonogenicity, and spheroid growth in plasma-like media. Genetic inhibition of AHR reduces tumor burden and metastatic competence in xenograft models. These findings reveal a mechanistic link between oncogene fluctuation, amino acid metabolism, and immune evasion, positioning AHR as a central mediator of EwS progression and a tractable therapeutic vulnerability.

cancer biology↗

bioRxiv2025

A dual mechanism of sensitivity to PLK4 inhibition by RP-1664 in neuroblastoma

A novel therapeutic strategy was recently proposed for high-risk neuroblastoma carrying copy number gain of the TRIM37 gene: centriole loss upon inhibition of polo-like kinase 4 (PLK4), while tolerated by normal cells, induces aberrant mitotic spindle formation and p53-dependent cell death in TRIM37-overexpressing cells. Interestingly, while full PLK4 inhibition causes centriole loss, partial inhibition is known to elevate centriole numbers. Here we show using a novel selective PLK4 inhibitor RP-1664 that both centriole loss and amplification contribute to hypersensitivity of neuroblastoma cells. Whereas inactivation of TRIM37 and TP53 rescues neuroblastoma cell death at higher concentrations of RP-1664, at lower doses cell death is TRIM37/TP53-independent. With CRISPR screens and live cell imaging we demonstrate that upon centriole amplification, neuroblastoma cells succumb to multipolar mitoses due to inability to cluster or inactivate supernumerary centrosomes. In vivo, RP-1664 shows robust efficacy in neuroblastoma xenografts at doses consistent with centriole amplification. STATEMENT OF SIGNIFICANCEHigh-risk neuroblastoma is associated with poor outcomes in pediatric patients and novel therapies need to be developed. We show that neuroblastoma cells are remarkably sensitive to PLK4 inhibitors due to a combination of two complementary mechanisms, supporting the evaluation of PLK4 inhibitors in clinical trials of high-risk neuroblastoma.

cancer biology↗

bioRxiv2025

High Tau Expression Correlates with Reduced Invasion and Prolonged Survival in Ewing Sarcoma

The microtubule-associated protein Tau (encoded by the MAPT gene) is linked to a family of neurodegenerative disorders defined as tauopathies, which are characterized by its brain accumulation in neurofibrillary tangles and neuropil threads. Newly described Tau functions comprise DNA protection, chromatin remodeling, p53 regulation and cell fate modulation, suggesting a role of Tau in oncogenesis. Bioinformatic-supported characterization of Tau in cancer reveals robust expression in bone cancer cells, in particular Ewing sarcoma (EwS) cell lines. EwS is an aggressive cancer caused by a fusion of members of the FET and ETS gene families, primarily EWSR1::FLI1. Here we found that MAPT is a EWSR1::ETS target gene and that higher Tau expression in EwS cells inhibited their migratory and invasive behavior, consistent with a more immobile and proliferative phenotype observed in EwS. Indeed, we report that high Tau expression is associated with improved overall survival of EwS patients. We also show that the sessile but proliferative phenotype of EWSR1::ETS-high cells may result from a modulatory role of Tau on focal adhesion to extracellular matrix proteins. Our data highlight the utility of determining Tau expression as a prognostic factor in EwS as well as the opportunity to target Tau expression as an innovative EwS therapy.

cancer biology↗

bioRxiv2025

Neural correlates of approach and avoidance tendencies toward physical activity and sedentary stimuli: An fMRI study

Automatic tendencies toward physical activity and sedentary stimuli are involved in the regulation of physical activity behavior. However, the brain regions underlying these automatic tendencies remain largely unknown. Here, we used an approach-avoidance task and magnetic resonance imaging (MRI) in 42 healthy young adults to investigate whether cortical and subcortical brain regions underpinning reward processing and executive function are associated with these tendencies. At the behavioral level, results showed more errors in avoidance behavior following sedentary stimuli than physical activity stimuli. At the brain level, avoidance behavior following sedentary stimuli was associated with more activation of the motor control network (dorsolateral-prefrontal cortex, primary and secondary motor cortices, somatosensory cortex). In addition, increased activation of the bilateral parahippocampal gyrus -- and structural deformation of the right hippocampus - were associated with a tendency toward approaching sedentary stimuli. Together, these results suggest that avoiding sedentary stimuli requires higher levels of behavioral control than avoiding physical activity stimuli.

neuroscience↗

bioRxiv2024

Metabolic PCTA-Based Shift Reagents for the Selective Detection of Extracellular Lactate Using CEST MRI

Lactate is a key metabolic driver in oncology and immunology. Even in the presence of physiological oxygen levels, most cancer cells upregulate anaerobic glycolysis, resulting in abnormal lactate production and accumulation in the tumor microenvironment. The development of more effective, sensitive, and safe probes for detecting extracellular lactate holds the potential to impact cancer metabolic profiling and staging significantly. Macrocyclic-based PARACEST agents have been reported to act as shift reagents (SRs) and detect extracellular lactate via CEST MRI. Here, we introduce a new family of SRs based on the PCTA ligand, an inherently stable and kinetically inert group of molecules with the potential for (pre)clinical translation. We observed that Yb-PCTA and Eu-PCTA can significantly shift lactate -OH signals in CEST spectra. In vitro, CEST MRI experiments proved that imaging extracellular lactate with these complexes is feasible and maintains high specificity even in the presence of competing small metabolites in blood and the tumor microenvironment. In vivo, preclinical imaging demonstrated that Yb-PCTA can be safely administered intravenously in mice to detect extracellular lactate non-invasively. This work represents a significant step towards precision and molecular imaging, demonstrating that the PCTA-ligand is a promising scaffold for developing molecular imaging sensors. These chemical sensors have broad medical applications, particularly in oncology and physiology.

biochemistry↗

bioRxiv2024

Uncovering nitroxoline activity spectrum, mode of action and resistance across Gram-negative bacteria

Nitroxoline is a bacteriostatic quinoline antibiotic, considered a metal chelator inhibiting the activity of RNA-polymerase1. Its clinical indications are limited to uncomplicated urinary tract infections (UTIs), with a clinical susceptibility breakpoint only available for Escherichia coli2. By testing > 1,000 clinical isolates, here we demonstrate a much broader activity spectrum and species-specific bactericidal activity, including multidrug-resistant Gram-negative bacteria for which therapeutic options are limited due to resistance. By combining systematic genetic and proteomic approaches with direct measurement of intracellular metals, we dissect nitroxoline perturbation of metal homeostasis and unveil additional effects on bacterial physiology. We show that nitroxoline affects outer membrane integrity, synergizing with large-scaffold antibiotics and resensitizing colistin-resistant Enterobacteriaceae in vitro and in vivo. We further characterise resistance mechanisms across E. coli, Acinetobacter baumannii and Klebsiella pneumoniae, recapitulating known E. coli resistance determinants and uncovering novel and conserved mechanisms across species, demonstrating their common effect on nitroxoline efflux.

microbiology↗

bioRxiv2024

Systematic analysis of gut bacterial carcinogen metabolism and its functional consequences

Organic carcinogens, in particular DNA-reactive compounds, contribute to the irreversible initiation step of tumorigenesis through introduction of genomic instability. Although carcinogen bioactivation and detoxification by human enzymes has been extensively studied, carcinogen biotransformation by human-associated bacteria, the microbiota, has not yet been systematically investigated. We tested the biotransformation of 68 mutagenic carcinogens by 34 bacterial species representative for the upper and lower human gastrointestinal tract and found that the majority (41) of the tested carcinogens undergo bacterial biotransformation. To assess the functional consequences of microbial carcinogen metabolism, we developed a pipeline to couple gut bacterial carcinogen biotransformation assays with Ames mutagenicity testing and liver biotransformation experiments. This revealed a bidirectional crosstalk between gut microbiota and host carcinogen metabolism, which we validated in gnotobiotic mouse models. Overall, the systematic assessment of gut microbiota carcinogen biotransformation and its interplay with host metabolism highlights the gut microbiome as an important modulator of exposome-induced tumorigenesis.

microbiology↗

bioRxiv2024

Two-brain microstates: A novel method for quantifying task-driven inter-brain asymmetry

BackgroundThe neural mechanisms underlying real-time social interaction remain poorly understood. While hyperscanning has emerged as a popular method to better understand inter-brain mechanisms, inter-brain methods remain underdeveloped, and primarily focused on inter-brain synchronization (IBS). New methodWe developed a novel approach employing two-brain EEG microstates, to investigate neural mechanisms during symmetric and asymmetric interactive tasks. Microstates are quasi-stable configurations of brain activity that have been proposed to represent basic building blocks for mental processing. Expanding the microstate methodology to dyads of interacting participants enables us to investigate quasi-stable moments of inter-brain synchronous and asymmetric activity. ResultsConventional microstates fitted to individuals were not related to the different interactive conditions. However, two-brain microstates were modulated in the observer-actor condition, compared to all other conditions where participants had more symmetric task demands, and the same trend was observed for the follower-leader condition. This indicates differences in resting state default-mode network activity during interactions with asymmetric tasks. Comparison with existing methodsHyperscanning studies have primarily estimated IBS based on functional connectivity measures. However, localized connections are often hard to interpret on a larger scale when multiple connections across brains are found to be important. Two-brain microstates offer an alternative approach to evaluate neural activity from a large-scale global network perspective, by quantifying task-driven asymmetric neural states between interacting individuals. ConclusionsWe present a novel method using two-brain microstates, including open-source code, which expands the current hyperscanning-EEG methodology to measure and potentially identify both synchronous and asymmetric inter-brain states during real-time social interaction.

neuroscience↗

bioRxiv2024

Glutaredoxin 3 (GLRX3) confers a fusion oncogene-dependent vulnerability to Ewing sarcoma

Ewing sarcoma (EwS) is a highly aggressive bone and soft-tissue associated cancer for which there are no effective targeted therapeutics available. Genetically, EwS is driven by aberrantly active EWSR1::ETS fusion transcription factors, most commonly EWSR1::FLI1. Despite their unique expression in EwS, all attempts to effectively target these fusion oncoproteins clinically were not yet successful, wherefore alternative targets are required. Here, we functionally characterize the evolutionarily conserved oxidative stress regulator glutaredoxin 3 (GLRX3) as a EwS-specific and EWSR1::FLI1-dependent vulnerability. Through integration of transcriptome-profiling, conditional drug screens in 3D cultures, and functional experiments, we discover that GLRX3 promotes EwS growth in vitro and in vivo, and that it has a key role in mitigation of oxidative stress and maintenance of iron homeostasis. These GLRX3 functions can be exploited in both GLRX3-high and -low expressing EwS cells by targeted therapeutics including CDK4/6 inhibitors and inducers of apoptotic and ferroptotic cell death. Collectively, our results exemplify how the interplay of an evolutionarily conserved oxidative stress regulator with a dominant oncogene can promote malignancy but provide opportunities for predictive diagnostics and personalized therapy.

cancer biology↗

bioRxiv2024

Podocyte exopher-formation as a novel pathomechanism in membranous nephropathy

BackgroundMembranous nephropathy (MN) is caused by autoantibody binding to podocyte foot process antigens such as THSD7A and PLA2R1. The mechanisms of the glomerular antigen/autoantibody deposition and clearance are unknown. MethodsWe explore the origin and significance of glomerular accumulations in (1) diagnostic and follow-up biospecimens from THSD7A+ and PLA2R1+-MN patients compared to nephrotic non-MN patients, and (2) in experimental models of THSD7A+-MN. ResultsWe discovered podocyte exophers as correlates of histological antigen/autoantibody aggregates found in the glomerular urinary space of MN patients. Exopher vesicle formation represents a novel form of toxic protein aggregate removal in Caenorhabditis elegans neurons. In MN patients, podocytes released exophers to the urine. Enrichment of exophers from MN patient urines established them as a glomerular exit route for antigens and bound autoantibody. Exophers also carried disease-associated proteins such as complement and provided a molecular imprint of podocyte injury pathways. In experimental THSD7A+-MN, exophers were formed from podocyte processes and cell body. Their formation involved the translocation of antigen/autoantibody from the subepithelial to the urinary side of podocyte plasma membranes. Urinary exopher-release correlated with lower albuminuria and lower glomerular antigen/autoantibody burden. In MN patients the prospective monitoring of urinary exopher abundance and of exopher-bound autoantibodies was additive in the assessment of immunologic MN activity. ConclusionsExopher-formation and release is a novel pathomechanism in MN to remove antigen/autoantibody aggregates from the podocyte. Tracking exopher-release will add a non-invasive diagnostic tool with prognostic potential to clinical diagnostics and follow-up of MN patients.

cell biology↗

bioRxiv2024

Unraveling interindividual differences and functional consequences of gut microbial metabolism of immunosuppressants

A major challenge in kidney transplantation (KT) is the large interpatient variability in the pharmacokinetics of immunosuppressive drugs. Here, we explored the role of the gut microbiome in interindividual variation in immunosuppressive drug metabolism. Analysis of 38 fecal communities, including 10 from KT recipients, and 45 bacterial species against 25 drugs, revealed significant interindividual and drug-specific differences in metabolism. Notably, 15 of 16 immunosuppressants tested were metabolized by at least one microbial community, and we found specific bacterial species, such as Bacteroides uniformis, to be potent metabolizers. We identified 18 different metabolites for 16 drugs, including two previously undescribed metabolites for sirolimus and everolimus. Our study reveals the functional impact of microbial metabolism on key immunosuppressants, including inactivation of tacrolimus, activation and potential increase in toxicity of mycophenolate mofetil (MMF), and shows that the microbial metabolite of methylprednisolone exhibits a 2.6-fold increase in epithelial permeability compared to the parent drug. Through a gain-of-function genetic screen we identified the B. uniformis enzyme BACUNI_RS05305 to be responsible for MMF activation. Using machine learning to model microbial community drug metabolism, abundance features of prevalent species predicted the biotransformation of some drugs well, while for others, a priori experimental information on bacterial genes and enzyme protein structures led to improved predictions. Our research highlights the potential of gut microbiome features to explain interindividual variability in immunosuppressive therapies and sets the stage for clinical trials to identify microbiome-encoded signatures predictive of drug metabolism in KT patients. One Sentence SummaryThis study reveals interindividual variability in gut microbial metabolism of immunosuppressive drugs mediated by specific bacterial species and enzymes.

microbiology↗

bioRxiv2024

Pervasive sublethal effects of agrochemicals as contributing factors to insect decline

Insect biomass is declining across the globe at an alarming rate. Climate change and the widespread use of pesticides have been hypothesized as two underlying drivers. However, the lack of systematic experimental studies across chemicals and species limits our causal understanding of this problem. Here, we employed a chemical library encompassing 1024 different molecules--including insecticides, herbicides, fungicides, and plant growth inhibitors --to investigate how insect populations are affected by varying concentrations of pesticides, focusing on sublethal doses. Using a controlled laboratory pipeline for Drosophila melanogaster, we found that 57% of these chemicals affect the behavior of larvae at sublethal concentrations, and an even higher proportion compromises long-term survivability after acute exposure. Consistent with these results, we observed that exposure to chemicals at doses orders of magnitude below lethality induced widespread phosphorylation changes across the larval proteome. The effects of agrochemicals were amplified when the ambient temperature was increased by four degrees. We also tested the synergistic effects of multiple chemicals at doses found widely in nature and observed fitness-reducing changes in larval developmental time, behavior, and reproduction. Finally, we expanded our investigation to additional fly species, mosquitos, and butterflies and detected similar behavioral alterations triggered by pesticides at sublethal concentrations. Our results provide experimental evidence that strongly suggests sublethal doses of agrochemicals coupled with changes in environmental temperatures are contributing to the global decline in insect populations. We anticipate that our assays can contribute to improving chemical safety assessment, better protect the environment, secure food supplies, and safeguard animal and human health, as well as understand our rapidly changing world.

ecology↗

bioRxiv2023

Deep quantitative glycoproteomics reveals gut microbiome induced remodeling of the brain glycoproteome

HighlightsO_LIHigh throughput glycoproteomics method with multiplexed quantification C_LIO_LI25-fold improvement of the mouse brain glycoproteome coverage C_LIO_LIStructural features dictate level of glycosite micro-heterogeneity C_LIO_LIGut microbiome composition extensively impacts the brain glycoproteome C_LIO_LIModulation of glycosylation is site-specific C_LI Protein glycosylation is a highly diverse post-translational modification, modulating key cellular processes such as cell signaling, adhesion and cell-cell interactions. Its deregulation has been associated with various pathologies, including cancer and neurological diseases. Methods capable of quantifying glycosylation dynamics are essential to start unraveling the biological functions of protein glycosylation. Here we present Deep Quantitative Glycoprofiling (DQGlyco), a method that combines high-throughput sample preparation, high-sensitivity detection, and precise multiplexed quantification of protein glycosylation. We used DQGlyco to profile the mouse brain glycoproteome, in which we identify 158,972 and 15,056 unique N- and O-glycopeptides localized on 3,199 and 2,365 glycoproteins, respectively - this amounts to 25-fold more glycopeptides identified compared to previous studies. We observed extensive heterogeneity of glycoforms and determined their functional and structural preferences. The presence of a defined gut microbiota resulted in extensive remodeling of the brain glycoproteome when compared to that of germ-free animals, exemplifying how the gut microbiome may affect brain protein functions.

molecular biology↗

bioRxiv2023

Inhibition of Notch activity by phosphorylation of CSL in response to parasitization in Drosophila

Notch signalling activity regulates hematopoiesis in Drosophila and vertebrates alike. Parasitoid wasp infestation of Drosophila larvae, however, requires a timely downregulation of Notch activity to allow the formation of encapsulation-active blood cells. Here we show that the Drosophila CSL transcription factor Suppressor of Hairless [Su(H)] is phosphorylated at Serine 269 in response to parasitoid wasp infestation. As this phosphorylation interferes with the DNA-binding of Su(H), it reversibly precludes its activity. Accordingly, phospho-deficient Su(H)S269A mutants are immune compromised. A screen for kinases involved in Su(H) phosphorylation identified Pkc53E, required for normal hematopoiesis as well as for parasitoid immune response. Genetic and molecular interactions support the specificity of the Su(H)-Pkc53E relationship. Moreover, phorbol ester treatment inhibits Su(H) activity in vivo and in human cell culture. We conclude that Pkc53E targets Su(H) during parasitic wasp infestation, thereby remodeling the blood cell population required for wasp egg encapsulation.

developmental biology↗