Nature Cell Biology

Restoration of organellar membrane integrity is critical for maintaining cellular homeostasis. Lysosomal membrane damage activates local repair machineries and global stress responses, but how signaling lipid metabolism is engaged by damage sensors to support and mechanistically link these processes remains poorly understood. Here we show that the phosphoinositide 3-phosphatase MTMR14 is recruited to damaged lysosomes through calcium-dependent binding to sphingomyelin. At these sites, MTMR14 promotes local PI(3)P hydrolysis and supports PI(4)P accumulation, thereby facilitating formation of ER-lysosome contact sites associated with membrane repair, without affecting ESCRT recruitment. MTMR14-dependent lipid remodelling causes reduced mTORC1 signalling and a decrease in global protein synthesis, consistent with an acute proteostatic adaptation to lysosomal injury. Cells lacking MTMR14 display impaired damage-induced lipid remodelling, altered repair-associated structures, sustained protein synthesis, and increased sensitivity to lysosomal injury, all of which can be mitigated by mTORC1/S6K inhibition. Our findings identify damage-sensing recruitment of MTMR14 and local PI(3)P turnover on damaged lysosomes as a phosphoinositide module that promotes lysosomal membrane integrity and homeostasis while functionally linking nutrient signalling to proteostasis under membrane stress.

Autophagy is essential for CD4+ T cell activation and immune regulation. However, during activation both autophagy and anabolic signaling must be simultaneously sustained, challenging established models of pathway antagonism. Here, we show that T cell receptor signaling and co-stimulation induce a non-canonical form of autophagy required for proliferation and cytokine production. Pharmacological and genetic analyses reveal that this pathway is activated concurrently with mTORC1, and is dependent on PIK3C3, but occurs independently of the canonical regulators ULK1/2, AMPK, ATG13, and Beclin 1. Furthermore, immuno-electron microscopy demonstrates that activation generates smaller autophagic structures that associate with multivesicular bodies and exhibit a unique morphology. These findings uncover a fundamental rewiring of autophagy control in CD4+ T cells and identify a novel form of mechanistically and morphologically distinct non-canonical autophagy.

P-bodies are cytoplasmic membraneless organelles involved in mRNA storage, yet their role in cellular stress responses remains poorly understood. Here, we demonstrate that P-bodies are rapidly and selectively remodeled during the early response to endoplasmic reticulum (ER) stress in D. melanogaster oogenesis, positioning them as key early stress responders. Notably, this remodeling occurs within minutes of stress induction and precedes stress granule formation. This early remodeling is characterized by changes in P-body morphology and internal organization and promotes selective mRNA regulation. Specifically, ER stress leads to the recruitment and stabilization of maternal mRNAs and those encoding P-body components, while transcripts not associated with P-bodies are degraded. These observations indicate that P-body remodeling is not merely structural but functionally linked to the selective preservation of mRNA populations during stress. Mechanistically, we find that this process is driven by transcriptional upregulation of the RNA-binding protein, Bruno 1, downstream of ATF4-dependent stress signaling, thereby establishing a direct connection between the unfolded protein response and condensate regulation. Consistent with this model, loss of Bruno 1 abolishes, whereas its overexpression enhances P-body remodeling, demonstrating that stress-induced changes in RNA binding protein levels can actively reprogram condensate properties. Together, our findings reveal that P-bodies function as dynamic, stress-responsive hubs that integrate transcriptional signaling with post-transcriptional control, enabling the selective preservation of essential mRNAs during ER stress. More broadly, this work uncovers a previously unrecognized mechanism by which stress signaling pathways reorganize cytoplasmic architecture to shape mRNA fate.

Lysosomal enzymes are synthesized in the Endoplasmic Reticulum (ER) and transported to lysosomes to execute their functions. Deficiencies in lysosomal enzymes or components of the lysosomal transport machinery result in lysosomal storage disorders. While mannose-6-phosphate mediated lysosomal enzymes sorting in the Golgi has been extensively characterized, the mechanisms governing their export from the ER remain elusive. Here, we show that de novo lipogenesis, a metabolic pathway responsible for fatty acid synthesis, regulates lysosomal enzyme transport. Inhibition of de novo lipogenesis leads to the retention of lysosomal enzymes within the ER. Mechanistically, fatty acid derived from de novo lipogenesis is used for Arf1 myristoylation. Myristoylated Arf1 promotes retrograde vesicle trafficking from the Golgi to the ER, thereby maintaining the homeostatic bidirectional flux required for efficient ER export of lysosomal enzymes. Our findings uncover a critical functional link between lipid metabolism and lysosomal enzyme trafficking.

Liver injury induces rapid transcriptional responses in hepatocytes, yet the chromatin features that distinguish injured hepatocytes from healthy hepatocytes remain poorly understood. Using an integrated functional genomics approach combining bulk RNA-seq, ATAC-seq, and CUT&Tag profiling of H3K27ac and H3K27me3, we define the transcriptional and chromatin landscape of Sox9-expressing hepatocytes, which exhibit gene expression consistent with both hepatocyte and biliary identity. Under homeostatic conditions, Sox9+ hybrid hepatocytes (HybHeps) are rare and confined to the periportal space, while chronic injury induces an expansion of Sox9+ metaplastic hepatocytes (MetHeps). We identify three classes of differentially expressed genes associated with injury-responsive, state-associated, or shared regulatory programs and demonstrate that these classes are governed by distinct chromatin mechanisms. Injury-responsive transcription is driven primarily by dynamic chromatin accessibility remodeling at NF-{kappa}B- and AP-1-enriched regulatory elements, while state-associated and shared programs are reinforced through selective H3K27ac and H3K27me3 modification with comparatively stable accessibility. Relative to conventional hepatocytes, HybHeps encode a permissive chromatin landscape at injury-responsive loci under homeostatic conditions, consistent with epigenetic priming that facilitates rapid inflammatory activation. Projection of mouse-derived gene programs onto a human liver single-cell atlas encompassing both healthy and diseased hepatocytes confirms that SOX9-expressing hepatocytes preferentially engage injury-associated inflammatory modules while attenuating hepatocyte metabolic identity programs. Together, these findings define a chromatin-based regulatory dichotomy between inflammatory responsiveness and hybrid hepatocyte cell state stability, providing mechanistic insight into how differentiated epithelial cells integrate inflammatory signals while preserving cell state.

Ferroptosis is driven by iron-dependent lipid peroxidation, yet how metabolic flux through central lipid pathways is selectively routed towards pro-ferroptotic lipid species remains unclear. Here, through an unbiased chemical-genetic screen targeting core metabolic enzymes, we identify diacylglycerol (DAG) as a licensing lipid intermediate whose pro-ferroptotic activity depends on its intracellular routing. Systematic manipulation of lipolytic flux reveals that ferroptotic vulnerability is not determined by bulk lipolytic output or downstream intermediates, but by the selective channelling of DAG into a distinct metabolic fate. Mechanistically, DAG is selectively routed through a previously unrecognized intracellular metabolic axis composed of choline phosphotransferase 1 (CHPT1) and lecithin-cholesterol acyltransferase (LCAT). We uncover an enzymatically active intracellular pool of LCAT (iLCAT) that cooperates with CHPT1 on Golgi-trans-Golgi network membranes to generate polyunsaturated cholesteryl esters that execute ferroptosis. Functionally, enforced DAG routing through this axis suppresses tumour growth via ferroptosis in vivo, whereas hepatocyte-specific inhibition of the CHPT1-iLCAT axis attenuates lipid peroxidation and disease progression in metabolic dysfunction-associated steatohepatitis. Together, these findings establish subcellular lipid routing, rather than lipid abundance per se, as a fundamental determinant of ferroptotic vulnerability.

How organelles communicate stress to the nucleus to coordinate adaptive responses remains a fundamental question in cell biology. Here, we identify a non-canonical retrograde signaling pathway in which stalling-induced UFMylation of ER-associated ribosomes anchors splicing regulators at the ER, directly coupling translational stress to nuclear RNA processing. Phylogenetic profiling linked the UFMylation machinery to a network of nuclear mRNA processing factors. Fractionation-based quantitative proteomics further supported this link and revealed that translational stress triggers UFM1-dependent retention of serine/arginine-rich (SR) splicing factors at the ER, depleting their nuclear pools. Mechanistically, UFMylated ribosomes physically tether SR proteins at the ER surface, driving widespread intron retention that preferentially targets transcripts encoding membrane lipid metabolism and endomembrane-associated processes--a response conserved from plants to mammals. These findings reframe UFMylation from a local ribosome repair signal to a systems-level coordinator of ER-nucleus communication that reprograms nuclear splicing and reshapes membrane-associated gene expression with implications for diverse human diseases linked to UFMylation defects.

Pluripotency and lineage commitment in embryonic stem cells emerge from transcriptional programs shaped by higher-order chromatin architecture and the integration of extracellular matrix (ECM) cues, yet the molecular basis of this coordination remains unresolved. Here we identify nuclear {beta}-actin as a central regulator coupling chromatin organization to ECM-dependent control of cell fate in mouse embryonic stem cells. CRISPR/Cas9-mediated ablation of {beta}-actin leads to loss of core pluripotency factors, including Oct4 and Sox2, and drives widespread transcriptional reprogramming, whereas nuclear-targeted re-expression restores these defects. Genome-wide chromatin accessibility profiling reveals a pronounced reduction at regulatory elements of pluripotency genes, consistent with impaired chromatin remodeling. In parallel, ECM gene programs are aberrantly activated, resulting in altered matrix composition, increased stiffness heterogeneity and disrupted cellular biomechanics. Functionally, these changes compromise self-renewal, bias lineage specification and impair differentiation capacity, notably blocking neuronal differentiation while promoting mesodermal-like fates. In vivo, {beta}-actin depletion markedly restricts teratoma growth and disrupts tri-lineage potential. Reintroduction of nuclear {beta}-actin restores chromatin accessibility, transcriptional programs, ECM properties and differentiation competence. Together, our findings position nuclear {beta}-actin as a key integrator of genome architecture, mechanotransduction and transcription, thereby linking chromatin state to ECM-dependent regulation of stem cell identity.

Cell nuclei are often used to assess cell health, but how their shapes vary in normal tissues and how they respond to mechanical forces is not well understood. Here, we describe deep invaginations of the nuclear envelope (DINEs) as common features of epithelial cell nuclei. After their formation, DINEs exist independently of the cytoskeleton, depend on A-type lamins, and emerge in response to cell crowding, contact inhibition, and tissue maturation. High-resolution imaging shows that, in contrast to the peripheral nuclear lamina, DINEs contain densely packed chromatin with regions of active gene transcription. They also remodel dynamically during confined migration, allowing nuclei to adapt to physical constraints. Mechanistically, DINE formation is linked to suppression of MAPK signaling, while activation of growth-promoting pathways reduces their occurrence. These findings reveal DINEs as intrinsic, mechanosensitive structures that coordinate nuclear shape, chromatin organization, and gene activity, providing new insight into how epithelial cells integrate mechanical and biochemical cues to maintain tissue homeostasis. TeaserDeep nuclear envelope invaginations organize chromatin and gene activity in response to epithelial crowding.

Differentiation of epidermal keratinocytes is accompanied by profound reorganization of intracellular architecture, but how organelle remodeling interfaces with cell fate control is not well understood. Here, we generate a compartment-resolved proteomic map of keratinocyte differentiation and identify extensive remodeling of lysosomes, mitochondria, autophagic vesicles, plasma membrane, and nucleus. Differentiating keratinocytes display coordinated enrichment of lysosomal degradative machinery, vesicular trafficking factors, and mitochondrial metabolic proteins, revealing organelle remodeling as a prominent feature of epidermal differentiation. From the lysosomal proteome, we identify Sorting Nexin 3 (SNX3) as a critical regulator of epidermal homeostasis. SNX3 increasingly localizes to LAMP1-positive vesicles during differentiation, and its loss impairs epidermal differentiation, suppresses Notch signaling, and promotes proliferative gene expression. In vivo, SNX3-deficient skin grafts fail to maintain normal epidermal architecture and instead develop into squamous cell carcinoma. Mechanistically, SNX3 mediates efficient Notch receptor activation, as SNX3 loss reduces nuclear Notch1 and NICD production, whereas NICD re-expression can rescue the differentiation defect. Our study defines a proteomic framework for organelle remodeling during epidermal differentiation and identifies lysosome-associated SNX3 as a key link between endolysosomal trafficking, Notch signaling, and epidermal tissue homeostasis.

The nucleolus is essential for ribosome biogenesis and cellular homeostasis, and its dysfunction can induce nucleolar stress, which has been implicated in cancer and other diseases. However, nucleolar stress is commonly inferred from morphological alterations or a limited set of functional assays, and quantitative approaches based on gene expression profiles remain lacking. Here, we integrate literature curation with multi-dataset screening to define a nucleolar stress gene signature and develop a nucleolar stress score (NuS) that is applicable across bulk transcriptomics, single-cell transcriptomics, proteomics, and spatial transcriptomics. Using this framework, we show in colorectal cancer models that oxaliplatin induces nucleolar stress, suppresses nascent rRNA synthesis, and activates p53 signalling, whereas these responses are attenuated in oxaliplatin-resistant cells. In combination with a ribosome biogenesis activity score (RiboSis), NuS captures related yet distinct dimensions of nucleolar function and stratifies tumors into functional states associated with distinct clinical outcomes. Furthermore, NuS-based analysis of perturbational transcriptomes enables prioritization of compounds with putative nucleolar stress-inducing activity. Collectively, this study establishes a quantitative framework for evaluating nucleolar stress and illustrates its applications in disease stratification and drug mechanism discovery.

At birth, the intestine must rapidly adapt to enable nutritional function and immune microbial tolerance. Here, integrating single-cell multi-omics and spatial transcriptomics we define the circuits underpinning this process. We identify asynchronous developmental trajectories with postnatal epithelial reprogramming characterised by coordinated changes in metabolism, junctional structure and innate defence. At birth epithelial stem cells demonstrate dynamic enhancer remodelling, with accessibility often preceding transcription. Fetal stemness elements remain accessible despite reduced transcription across epithelial lineages, retaining plasticity potential. Post-natal epithelia experience sequential homing of myeloid cells followed by innate T cells with peri-epithelial B cells localising later in infancy. Using developmentally staged organoids, we show that epithelial responses to inflammatory stimuli are age-dependent and constrained in early life. We identify BHLHE40 as an early-life regulator that attenuates the impact of interferon- and NF-{kappa}B-driven signalling. Altogether we define the events driving epithelial licensing and barrier adaptation at birth and through infancy.

Neural stem cells (NSCs) sustain lifelong neurogenesis through the tight regulation of quiescence, self-renewal and differentiation. Quiescent NSCs (qNSCs) exist in distinct substates, ranging from deep to shallow quiescence, yet the mechanisms governing these transitions remain unclear. In long-term self-renewing NSCs of the adult zebrafish pallium, we show that mTORC1 activity is specifically enriched during a prolonged quiescence phase in which NSCs acquire activation competence. Functional perturbations, analyzed in situ and using single-cell RNA sequencing, reveal that mTORC1 regulates cell progression during this phase, concomitantly ensuring the correct tempo for NSC transition towards activation and the preservation of stemness. These findings challenge the classical view of mTORC1 as a simple regulator of proliferation and identify it as a key regulator of NSC quiescence heterogeneity and dynamics under physiological conditions. By coordinating stemness maintenance with activation competence, mTORC1 emerges as a central player balancing long-term NSC preservation with neurogenic output in the adult brain.

How endothelial cell-cell junctions integrate cytoskeletal, adhesive, and local signaling networks to maintain vascular barrier integrity remains incompletely defined. Here, we identify junctional cadherin 5-associated protein (JCAD) as a modular scaffold that organizes endothelial tight junction architecture by coupling junctional condensates to actin and RhoA signaling. Genetic deletion of Jcad in mice does not affect baseline vascular permeability but causes inflammation-dependent barrier hyperpermeability. JCAD depletion in primary human endothelial cells disrupts tight junction continuity and increases paracellular permeability. Mechanistically, JCAD localizes to ZO-1-positive tight junctions independently of VE-cadherin, directly binds filamentous actin, and forms dynamic actin-associated condensates at cell-cell contacts. Structure-function analysis reveals separable domains mediating tight junction targeting and actin binding, establishing a bipartite architecture that distinctly coordinates junctional signaling and cytoskeletal coupling. Together, these findings identify JCAD as a cell-cell adhesion scaffold that integrates the phase-separated tight junction plaque with actin and RhoA-dependent mechanics, enabling endothelial barrier adaptation to inflammatory stress.

The endolysosomal system is crucial for the degradation of cellular waste in the lysosomal lumen. Within this pathway, endosomes mature prior to their fusion with lysosomes. This process relies on the sequential action of the CORVET and HOPS tethering complexes, guided by Rab5 and Rab7 GTPases, respectively. CORVET acts on early endosomes (EEs), transitioning to HOPS on maturing late endosomes/multivesicular bodies (LEs/MVBs) for lysosomal fusion. This process is finely tuned by the Rab activating guanine nucleotide exchange factor (GEF) and the inactivating GTPase activating protein (GAP). The BuMC1 GEF complex (Bulli-Mon1-Ccz1) uniquely activates Rab7 in metazoans and interacts with Rab5, which stimulates its activity. Here, we identified GAPsec as a novel GAP with activity for Rab5 required for endosomal maturation in fruit fly nephrocytes. Inactivation of GAPsec results in enlarged, dysfunctional endosomes that are unable to reach lysosomes for degradation. Our study highlights the importance of coordinated Rab regulation for efficient endosomal trafficking.

Chronic fibrotic disorders like idiopathic pulmonary fibrosis (IPF) are characterized by aberrant alveolar regeneration and severely limited treatment options. Identification of the mechanisms driving aberrant epithelial repair can lead to new viable therapeutic targets. Using integrated single nucleus ATAC- and RNA-sequencing on human lungs and an in vitro model of dysplastic repair, we identify two distinct regenerative trajectories for alveolar type 2 (AT2) cells: a resolvable euplastic repair trajectory and a persistent, non-resolving dysplastic repair trajectory. The latter is governed by a spatially restricted ITGB6/TGF{beta}1/SMAD3 signaling axis in fibrotic regions of IPF lungs and in murine lungs characterized by chronic epithelial remodeling. Mechanistically, SMAD3 directly regulates dysplastic transitional cell (DTC) markers, including KRT17 and Stratifin. We show that TGF{beta}1 signaling promotes a physical interaction between KRT17 and Stratifin at the leading edge of migrating DTCs in vitro and in vivo, which is essential for their migratory capacity. These findings collectively define the molecular regulation of AT2-driven dysplastic regeneration and identify TGF{beta}1-induced KRT17-Stratifin axis as a central driver of pathological epithelial remodeling in chronic fibrosis, which can be targeted therapeutically to tilt the balance in favor of euplastic regeneration.

Polyploid cells are increasingly recognized not only as hallmarks of cancer but also as features of regenerating tissues. During intestinal regeneration, polyploid cells are transient, yet the mechanisms underlying their clearance remain unknown. Using mouse intestinal organoids as a regeneration model, we show that, unlike in many cancer cell-line models, this clearance occurs without immediate cell-cycle arrest and is not driven by failure to establish spindle bipolarity. Instead, polyploid intestinal cells efficiently cluster supernumerary centrosomes to form bipolar spindles in an HSET-dependent manner, facilitated by delayed centrosome separation at mitotic onset. Despite this, polyploid divisions frequently produce chromosome segregation errors, including catastrophic chronocrisis. Lineage tracing reveals that progeny of such divisions is rapidly lost over subsequent generations. Increasing polyploidy during early regeneration disrupts organoid maturation, indicating that timely polyploidy clearance is required for successful regeneration. Polyploid cells are also detected in regenerating human colonic organoids, suggesting that transient polyploidy is a conserved feature of intestinal regeneration.

Protein aggregation, impaired degradation, and immune activation are central hallmarks of neurodegenerative diseases, yet how these processes are coordinated remains unclear. Here, we identify Immune-Protein Degradation Bodies (I-PDBs), a previously unrecognized class of BAG2-driven, phase-separated organelles that integrate protein quality control with adaptive immunity. IFN{gamma} induce I-PDB formation at the endoplasmic reticulum (ER), where they concentrate immunoproteasome components, MHC-I peptide-loading machinery, and ER-associated chaperones. I-PDBs redirect proteostatic cargo from centrosomal aggregation pathways to spatially restricted degradation sites optimized for antigenic peptide generation, coupling selective substrate clearance to CD8 T cell engagement. Using a cellular model of aggregation-prone tau, we show that I-PDBs capture pathological tau fibrils at ER-microtubule interfaces and process them into potentially antigenic peptides, thus reducing the load of aggregation-prone tau peptides. We term this mechanism the Proteostasis-Associated Immune Relay (PAIR), establishing I-PDBs as critical hubs linking proteostasis to immune surveillance with broad implications for disease. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/719751v1_ufig1.gif" ALT="Figure 1"> View larger version (58K): org.highwire.dtl.DTLVardef@16fa503org.highwire.dtl.DTLVardef@ba7607org.highwire.dtl.DTLVardef@19ae5bdorg.highwire.dtl.DTLVardef@60fdf7_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIIFN{gamma} drives BAG2-dependent Immune-Protein Degradation Bodies (I-PDBs) C_LIO_LII-PDBs assemble at the endoplasmic reticulum and are enriched in immunoproteasome and MHC-I machinery C_LIO_LII-PDBs shunt misfolded proteins, including pathological tau, away from aggresomes C_LIO_LII-PDBs couple proteostasis to antigen presentation, enhancing CD8 T cell recognition C_LIO_LIThe Proteostasis-Associated Immune Relay (PAIR) defines a pathway linking proteostasis to adaptive immunity C_LI

Intercellular organelle exchange is increasingly recognized as a feature of the tumor microenvironment, but whether tumor-derived mitochondria functionally shape anti-tumor T cell immunity remains unclear. Here we show that tumor-infiltrating CD8+ T cells acquire functional mitochondria from tumor cells through a contact-dependent, TCR-independent mechanism requiring the mitochondrial trafficking machinery Trak1-Miro1. Transferred tumor mitochondria enhanced CD8+ T cell effector activity, increasing cytotoxic molecule expression and tumor-cell killing. Mechanistically, tumor-derived mitochondria carried sphingosine-1-phosphate (S1P), which engaged S1PR1 signaling in recipient T cells. Tumor-specific deletion of Sphk2 diminished mitochondrial transfer-associated T cell activation, impaired CD8+ T cell effector function, and accelerated tumor progression in vivo. These findings reveal tumor-to-T cell mitochondrial transfer as an unexpected immunostimulatory circuit in the TME and identify mitochondrial SPHK2-S1P signaling as a regulator of CD8+ T cell anti-tumor function.

Primordial follicle oocyte activation (PFA) and zygotic genome activation (ZGA) represent two major waves of transcription activation respectively required for oocyte growth and preimplantation embryo development. Although many shared molecular hallmarks between PFA and ZGA suggest potential common factors and mechanisms driving both waves of transcriptional activation, such factors are yet to be identified. Here we demonstrate that the pioneer factor NFYA belongs to such regulators. Oocyte-specific Nfya deletion impairs open chromatin establishment and transcriptional activation during PFA, which triggers non-canonical ferroptosis leading to early folliculogenesis failure. Moreover, acute NFYA depletion in zygotes causes defective ZGA and predominantly two-cell embryo arrest. Mechanistically, although NFYA exhibits distinct chromatin-binding preferences predominantly targeting promoters during PFA and enhancers during ZGA, pre-occupied NFYA regulates chaperones and histone genes in both PFA and ZGA through conserved promoter binding. Together, our studies establish NFYA as a multifaceted regulator of genome activation during both PFA and ZGA. HighlightsO_LINFYA deficiency impairs primordial follicle oocyte activation (PFA) and triggers non-canonical ferroptosis resulting in early folliculogenesis failure C_LIO_LINFYA depletion impairs zygotic genome activation (ZGA) and causes predominantly 2-cell embryo arrest C_LIO_LIConserved and distinct NFYA-chromatin interactions drive both PFA and ZGA C_LIO_LIChaperones are pre-occupied and regulated by NFYA and their inhibition impairs both PFA and ZGA. C_LI