The intracellular trafficking pathway of transferrin

A novel way of regression of pregnant corpus luteum during parturition in mice: The ferroptosis associated with NCOA4-mediated ferritinophagy

Numerous studies have shown that inappropriate regression of corpus luteum would lead to adverse pregnancy outcomes during gestation. However, the detailed mechanisms and types of programmed cell death involved in the regression of pregnant corpus luteum are largely unknown. Here, we investigated whether ferroptosis and ferritinophagy were involved in luteal regression during parturition in mice and related mechanisms. The results showed that ferroptosis and ferritinophagy were both involved in luteal regression during mice peri-parturition in vivo. Erastin (ferroptosis agonist) treatment significantly accelerated luteal regression and induced premature labor in pregnant mice. PGF2α treatment induced the ferroptosis and ferritinophagy of luteal cells in vitro. Nevertheless, inhibition or promotion of ferroptosis significantly altered the states of PGF2α-induced luteal cell viability and ferroptosis. Furthermore, inhibition of autophagy (3-methyladenine co-treatment) alleviated PGF2α-induced ferritinophagy and ferroptosis of luteal cells, and knockdown of NCOA4 reduced the degradation of FTH1 and the level of ferroptosis of luteal cells induced by PGF2α. In summary, our current data demonstrated that the ferroptosis associated with NCOA4-mediated ferritinophagy was a novel way of luteal regression during peri-parturition in mice. Targeting ferroptosis in the corpus luteum may be a therapeutic strategy for preventing luteal insufficiency in the future.

Dual-Targeting Strategy to Repurpose Cetuximab with HFn Nanoconjugates for Immunotherapy of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a highly aggressive and treatment-resistant malignancy characterized by the lack of targeted therapies and poor clinical outcomes. Here, we present a dual-targeting strategy combining the anti-EGFR monoclonal antibody cetuximab (CTX) with H-ferritin (HFn), a nanoparticle targeting transferrin receptor 1 (TfR1), for potential immunotherapy in CTX-resistant tumors. The HFn-CTX nanoconjugate exhibited favorable biophysical properties and good tumor accumulation and significantly enhanced antibody-dependent cellular cytotoxicity (ADCC) in TNBC spheroids compared to CTX alone. Conversely, glioblastoma spheroids did not exhibit comparable reactivity. This effect correlated with elevated cell-surface EGFR expression and plasma-membrane lingering of the nanoconjugate in TNBC cells, facilitating robust immune activation. Biodistribution studies showed selective accumulation of the HFn-CTX nanoconjugate in TNBC tumors in vivo. These findings highlight the potential of HFn-CTX nanoconjugates to repurpose CTX for refractory cancers that express EGFR at high levels, such as TNBC, leveraging dual-receptor targeting to amplify immune-mediated cytotoxicity and overcome resistance.

Antisense oligonucleotides directed against App and Rab5 normalized endosomal Rab activity and reversed DS-AD-linked degenerative phenotypes in the Dp16 mouse model of Down syndrome

INTRODUCTION

Down syndrome (DS) markedly raises the risk of Alzheimer's disease (DS-AD). Our findings identified widespread dysregulation of the endolysosomal network (ELN) in DS and DS-AD brains, driven by increased APP gene dose, hyperactivation of RAB5, and elevated levels of guanine nucleotide exchange factors (GEFs) for RABs 7 and 11.

METHODS

We investigated whether increasing APP gene dose and RAB5 hyperactivation contributed to neuropathogenesis and whether a clinically feasible intervention could reverse ELN changes. The Dp16 DS-AD mouse model was treated with a mouse App-specific antisense oligonucleotide (App-ASO) and Rab5-specific ASOs targeting Rab5a and Rab5b.

RESULTS

App-ASO treatment normalized full-length APP (fl-APP) and its products, RAB5 activity, and downstream RABs 7 and 11 pathways. Rab5-ASOs reduced RAB5 levels and restored endosomal Rab activity. Both ASO treatments mitigated DS-AD-linked pathologies.

DISCUSSION

These findings highlight ELN dysregulation in DS and the therapeutic potential of ASO-based strategies targeting APP or Rab5 to counteract DS-AD features.

HIGHLIGHTS

App-ASO treatment reduced the levels of APP and its products and normalized endosomal Rab activity and GEF levels in Dp16 mice. Administration of Rab5-ASOs reduced RAB5 levels and normalized endosomal Rab activity and GEF levels in Dp16 mice. Both ASO treatments were well tolerated and mitigated APP-linked pathologies including tau hyperphosphorylation, neurotrophin signaling deficits, and synaptic protein loss. App-ASO or Rab5-ASOs reversed established pathological phenotypes in Dp16 mice.

Autophagy Impairment-Derived SQSTM1 Accumulation Promotes Ferroptosis in Corneal Epithelial Cells Through ACSL4 in Dry Eye

Purpose

To reveal the function of autophagy impairment-derived sequestosome 1 (SQSTM1) in inducing ferroptosis in an experimental dry eye model and investigate the underlying mechanism.

Methods

To induce the dry eye animal model, 8-week-old C57BL/6 mice were subcutaneously injected with scopolamine and exposed to a desiccated environment. To build the in vitro dry eye model, human corneal epithelial cells (HCECs) were applied with desiccating stress. Cell viability was examined using a CCK-8 kit. Intracellular reactive oxygen species (ROS), oxidative lipid, and Fe2+ were detected using the H2DCFDA assay kit, C11 BODIPY probe, and FerroOrange probe. Gene expression was screened by RNA sequencing. Protein expression was evaluated by western blot and immunofluorescence staining. Corneal defect area was assessed by fluorescein sodium staining. Conjunctiva goblet cells were counted by periodic acid-Schiff staining. Tear secretion was measured using phenol red cotton thread.

Results

Desiccating stress induced ferroptosis and SQSTM1 accumulation in both HCECs and C57BL/6 mice. SQSTM1 knockdown alleviated ferroptosis in HCECs. In contrast, the overexpression of SQSTM1 promoted ferroptotic changes. Additionally, overexpression of SQSTM1 significantly increased acyl-CoA synthetase long chain family member 4 (ACSL4). Also, targeted inhibition of ACSL4 mitigated the dry eye symptoms and ferroptosis caused by both SQSTM1 overexpression and desiccating stress.

Conclusions

The accumulation of SQSTM1 triggers corneal epithelial cells ferroptosis through ACSL4 in dry eye disease.

Downregulation of AATK enhances susceptibility to ferroptosis by promoting endosome recycling in gefitinib-resistant lung cancer cells

Ferroptosis has been characterised by disruption of the cell membrane through iron-related lipid peroxidation. However, regulation of iron homeostasis in lung cancer cells that are resistant to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) remains unclear. Transcriptome analysis identified a significant downregulation of apoptosis-associated tyrosine kinase (AATK) mRNA expression in gefitinib-resistant PC9 (PC9-GR) cells, which were found to be more susceptible to ferroptosis inducers. An in-depth analysis of publicly available datasets revealed that downregulation of AATK mRNA was associated with lymph node metastasis and poor prognosis in patients with lung adenocarcinoma. Knockdown of AATK-sensitised PC9, HCC827, and H441 cells to the ferroptosis inducer RSL3, whereas ectopic expression of AATK reduced RSL3-induced cell death in PC9-GR and HCC827-GR cells. Compared to PC9 cells, PC9-GR cells exhibited higher transferrin uptake, endosome recycling rate, and increased intracellular iron levels. Blocking iron transport reduced RSL3-induced ferroptosis in PC9-GR cells. Mechanistic studies showed that AATK localised to both early and recycling endosomes. Knockdown of AATK facilitated endosome recycling and elevated intracellular ferrous iron (Fe2+) levels in PC9 cells. Conversely, ectopic expression of AATK delayed endosome recycling and reduced intracellular Fe2+ levels in PC9-GR cells. Inhibition of AATK downregulation-induced iron accumulation decreased RSL3-induced ferroptosis. Taken together, our study indicates that the downregulation of AATK contributes to endosome recycling and iron accumulation, leading to an increased susceptibility to ferroptosis in EGFR-TKI-resistant lung cancer cells. © 2025 The Pathological Society of Great Britain and Ireland.

Trafficking of K63-polyubiquitin-modified membrane proteins in a macroautophagy-independent pathway is linked to ATG9A

Cytoplasmic K63-linked polyubiquitin signals have well-established roles in endocytosis and selective autophagy. However, how these signals help to direct different cargos to different intracellular trafficking routes is unclear. Here we report that, when the K63-polyubiquitin signal is blocked by intracellular expression of a high-affinity sensor (named Vx3), many proteins originating from the plasma membrane are found trapped in clusters of small vesicles that colocalize with ATG9A, a transmembrane protein that plays an essential role in autophagy. Importantly, whereas ATG9A is required for cluster formation, other core autophagy machinery as well as selective autophagy cargo receptors are not required. Although the cargos are sequestered in the vesicular clusters in an ATG9-dependent manner, additional signals are needed to induce LC3 conjugation. Upon removal of the Vx3 block, K63-polyubiquitylated cargos are rapidly delivered to lysosomes. These observations suggest that ATG9A plays an unexpected role in the trafficking of K63-polyubiquitin-modified membrane proteins.

Altered chaperone-nonmuscle myosin II interactions drive pathogenicity of the UNC45A c.710T>C variant in osteo-oto-hepato-enteric syndrome

The osteo-oto-hepato-enteric (O2HE) syndrome is a severe autosomal recessive disease ascribed to loss-of-function mutations in the Unc-45 myosin chaperone A (UNC45A) gene. The clinical spectrum includes bone fragility, hearing loss, cholestasis, and life-threatening diarrhea associated with microvillus inclusion disease-like enteropathy. Here, we present molecular and functional analysis of the UNC45A c.710T>C (p.Leu237Pro) missense variant, which revealed a unique pathogenicity compared with other genetic variants causing UNC45A deficiency. The UNC45A p.Leu237Pro mutant retained chaperone activity, prevented myosin aggregation, and supported proper nonmuscle myosin II (NMII) filament formation in patient fibroblasts and human osteosarcoma (U2OS) cells. However, the mutant formed atypically stable oligomers and prevented chaperone-myosin complex dissociation, thereby inhibiting NMII functions. Similar to biallelic UNC45A deficiency, this resulted in impaired intracellular trafficking, defective recycling, and abnormal retention of transferrin at various endocytic sites. In particular, coexpression of wild-type protein attenuated the pathogenic effects of the variant by inhibiting excessive oligomer formation. Our results elucidate the pathogenic mechanisms and recessive characteristics of this variant and may aid in the development of targeted therapies.

ATP8A1-translocated endosomal phosphatidylserine fine-tunes the multivesicular body formation and the endo-lysosomal traffic

P4-ATPases are phospholipid flippases responsible for the transbilayer lipid asymmetry. ATP8A1, a P4-ATPase family member, has been reported to be involved in phosphatidylserine (PS) translocation at the trans-Golgi network, early endosomes and recycling endosomes. However, the possible roles of the PS on late endosomes/lysosomes pathway and how they are regulated remain to be elucidated. This study showed enrichment of ATP8A1 in Rab7-positive late endosomal compartments, and that ATP8A1 primarily flips the endosomal PS from the luminal leaflet to the cytosolic leaflet but not the PS in the inner leaflet of the plasma membrane. ATP8A1 depletion accelerates the lysosome-destined cargo proteins transfer into the intraluminal vesicles (ILVs) of multivesicular bodies (MVBs) and alters the signaling of epidermal growth factor receptor. Mechanistically, ATP8A1 depletion leads to PS loading in the luminal leaflet of MVB's limiting membrane, which fine-tunes ILVs initiation and endosomal sorting complex required for transport (ESCRT) component recruitment.

The Na+-K+-ATPase alpha subunit is an entry receptor for white spot syndrome virus

White spot syndrome virus (WSSV) is a debilitating viral pathogen that poses a significant threat to the global crustacean farming industry. It has a wide host tropism because it uses several receptors to facilitate its attachment and entry. Thus far, not all the receptors have been identified. Here, we employed a BioID-based screening method to identify the Na+-K+-ATPase alpha subunit (PvATP1A) as a potential receptor in Penaeus vannamei. Although during the early stages of WSSV infection, PvATP1A was induced and underwent oligomerization, clustering, and internalization, knockdown of PvATP1A inhibited viral entry and replication. PvATP1A interacted with the WSSV envelope protein VP28 through its multiple extracellular regions, whereas synthetic PvATP1A extracellular region peptides blocked WSSV entry and replication. We showed that PvATP1A did not affect WSSV attachment but facilitated internalization via caveolin-mediated endocytosis and macropinocytosis. These findings provide a robust receptor screening approach that identified PvATP1A as an entry receptor for WSSV, presenting a novel target for the development of anti-WSSV therapeutics.

IMPORTANCE

Cell surface receptors are crucial for mediating virus entry into host cells. Identification and characterization of virus receptors are fundamental yet challenging aspects of virology research. In this study, a BioID-based screening method was employed to identify the Na+-K+-ATPase alpha subunit (PvATP1A) as a potential receptor for white spot syndrome virus (WSSV) in the shrimp Penaeus vannamei. We demonstrated that PvATP1A interacted with the WSSV envelope protein VP28 via its multiple extracellular regions, thereby promoting viral internalization through caveolin-mediated endocytosis and macropinocytosis. Importantly, compared with previously identified WSSV receptors such as β-integrin, glucose transporter 1 (Glut1), and polymeric immunoglobulin receptor (pIgR), PvATP1A demonstrated significantly enhanced viral entry, indicating that PvATP1A is a crucial entry receptor of WSSV. This study not only presents a robust approach for screening virus receptors but also identifies PvATP1A as a promising target for the development of anti-WSSV therapeutics.

Clathrin functions in intracellular sorting during receptor-mediated endocytosis

Clathrin is a key protein involved in receptor-mediated endocytosis (RME), which is also known as clathrin-mediated endocytosis (CME). Ligand/receptor binding facilitates clathrin clustering and cell surface invagination. We recently found that the typical CME ligand transferrin (Tf) can be internalized into cells without the clathrin heavy chain (CLTC). In this study, we clarified the unknown roles of clathrin during intracellular trafficking. Microscopic observation revealed that Tf accumulates in the deeper compartments of CLTC-knockdown HeLa cells. A colocalization analysis with endosome/lysosome markers showed that endocytosed Tf moves to early/late endosomes and then to lysosomes in CLTC-knockdown cells. This suggests that clathrin contributes to the recycling and exocytosis of endocytosed molecules.

Three signalling pathways for iron overload in osteoporosis: a narrative review

Osteoporosis is a metabolic bone disease characterized by a decrease in the amount of bone tissue per unit volume and changes in bone microstructure, often resulting in bone fragility and increased susceptibility to fracture. Iron plays an important role in the normal physiological activities of human body, and its abnormal metabolism is one of the risk factors of osteoporosis. Iron overload, as an abnormality of iron metabolism, has been reported to be associated with osteoporosis in recent years. However, the mechanism of iron overload involved in the process of osteoporosis is not fully understood. In this review, we summarize what we have learned about iron overload-associated bone loss from clinical studies and animal models. Starting from the three signaling pathways of Wnt/β-catenin, BMP/SMADs, PI3K/AKT/mTOR, the mechanism of iron overload affecting the process of osteoporosis was explored, we got the conclusion that iron overload accelerates the process of osteoporosis by inhibiting normal wnt signaling, suppressing the BMP-2/SMADs pathway, down-regulating the PI3K/AKT/mTOR pathway to inhibit bone formation, and destroying the bone strength and load-bearing capacity, which providing a new direction for clinical treatment.

Epsin1 enforces a condensation-dependent checkpoint for ubiquitylated cargo during clathrin-mediated endocytosis

Clathrin-mediated endocytosis internalizes proteins and lipids from the cell surface, supporting nutrient uptake, signaling, and membrane trafficking. Recent work has demonstrated that a flexible, liquid-like network of initiator proteins is responsible for catalyzing assembly of clathrin-coated vesicles in diverse organisms including yeast, mammals, and plants. How do cells regulate the assembly of this dynamic network to produce cargo-loaded vesicles? Here we reveal the ability of an endocytic adaptor protein, Epsin1, to conditionally stabilize the initiator protein network, creating a cargo-dependent checkpoint during clathrin-mediated endocytosis. Epsin1 is known to recruit ubiquitylated transmembrane proteins to endocytic sites. Using in vitro assays, we demonstrate that Epsin1 uses competitive binding and steric repulsion to destabilize condensation of initiator proteins in the absence of ubiquitin. However, when polyubiquitin is present, Epsin1 binds to both ubiquitin and initiator proteins, creating attractive interactions that stabilize condensation. Similarly, in mammalian cells, endocytic dynamics and ligand uptake are disrupted by removal of either ubiquitin or Epsin1. Surprisingly, when Epsin1 and ubiquitin are removed simultaneously, endocytic defects are rescued to near wildtype levels, although endocytic sites lose the ability to distinguish between ubiquitylated and non-ubiquitylated cargos. Taken together, these results suggest that Epsin1 tunes protein condensation to ensure the presence of ubiquitylated cargo during assembly of clathrin-coated vesicles. More broadly, these findings illustrate how a balance of attractive and repulsive molecular interactions controls the stability of liquid-like protein networks, providing dynamic control over key cellular events.

Nanoscale strategies: doxorubicin resistance challenges and enhancing cancer therapy with advanced nanotechnological approaches

Doxorubicin (DOX), an anthracycline, is widely used in cancer treatment by interfering RNA and DNA synthesis. Its broad antitumour spectrum makes it an effective therapy for a wide array of cancers. However, the prevailing drug-resistant cancer has proven to be a significant drawback to the success of the conventional chemotherapy regime and DOX has been identified as a major hurdle. Furthermore, the clinical application of DOX has been limited by rapid breakdown, increased toxicity, and decreased half-time life, highlighting an urgent need for more innovative delivery methods. Although advancements have been made, achieving a complete cure for cancer remains elusive. The development of nanoparticles offers a promising avenue for the precise delivery of DOX into the tumour microenvironment, aiming to increase the drug concentration at the target site while reducing side effects. Despite the good aspects of this technology, the classical nanoparticles struggle with issues such as premature drug leakage, low bioavailability, and insufficient penetration into tumours due to an inadequate enhanced permeability and retention (EPR) effect. Recent advancements have focused on creating stimuli-responsive nanoparticles and employing various chemosensitisers, including natural compounds and nucleic acids, fortifying the efficacy of DOX against resistant cancers. The efforts to refine nanoparticle targeting precision to improve DOX delivery are reviewed. This includes using receptor-mediated endocytosis systems to maximise the internalisation of drugs. The potential benefits and drawbacks of these novel techniques constitute significant areas of ongoing study, pointing to a promising path forward in addressing the challenges posed by drug-resistant cancers.

Harnessing macrophage-drug conjugates for allogeneic cell-based therapy of solid tumors via the TRAIN mechanism

Treatment of solid tumors remains challenging and therapeutic strategies require continuous development. Tumor-infiltrating macrophages play a pivotal role in tumor dynamics. Here, we present a Macrophage-Drug Conjugate (MDC) platform technology that enables loading macrophages with ferritin-drug complexes. We first show that macrophages actively take up human heavy chain ferritin (HFt) in vitro via macrophage scavenger receptor 1 (MSR1). We further manifest that drug-loaded macrophages transfer ferritin to adjacent cancer cells through a process termed 'TRAnsfer of Iron-binding protein' (TRAIN). The TRAIN process requires direct cell-to-cell contact and an immune synapse-like structure. At last, MDCs with various anti-cancer drugs are formulated with their safety and anti-tumor efficacy validated in multiple syngeneic mice and orthotopic human tumor models via different routes of administration. Importantly, MDCs can be prepared in advance and used as thawed products, supporting their clinical applicability. This MDC approach thus represents a promising advancement in the therapeutic landscape for solid tumors.

Transferrin receptor targeting chimeras for membrane protein degradation

Cancer cells require high levels of iron for rapid proliferation, leading to significant upregulation of cell-surface transferrin receptor 1 (TfR1), which mediates iron uptake by binding to the iron-carrying protein transferrin1-3. Leveraging this phenomenon and the fast endocytosis rate of TfR1 (refs. 4,5), we developed transferrin receptor targeting chimeras (TransTACs), a heterobispecific antibody modality for membrane protein degradation. TransTACs are engineered to drive rapid co-internalization of a target protein of interest and TfR1 from the cell surface, and to enable target protein entry into the lysosomal degradation pathway. We show that TransTACs can efficiently degrade a diverse range of single-pass, multi-pass, native or synthetic membrane proteins, including epidermal growth factor receptor, programmed cell death 1 ligand 1, cluster of differentiation 20 and chimeric antigen receptor. In example applications, TransTACs enabled the reversible control of human primary chimeric antigen receptor T cells and the targeting of drug-resistant epidermal growth factor receptor-driven lung cancer with the exon 19 deletion/T790M/C797S mutations in a mouse xenograft model. TransTACs represent a promising new family of bifunctional antibodies for precise manipulation of membrane proteins and targeted cancer therapy.

Self-Assembled DNA-Collagen Bioactive Scaffolds Promote Cellular Uptake and Neuronal Differentiation

Different modalities of DNA/collagen complexes have been utilized primarily for gene delivery studies. However, very few studies have investigated the potential of these complexes as bioactive scaffolds. Further, no studies have characterized the DNA/collagen complex formed from the interaction of the self-assembled DNA macrostructure and collagen. Toward this investigation, we report herein the fabrication of novel bioactive scaffolds formed from the interaction of sequence-specific, self-assembled DNA macrostructure and collagen type I. Varying molar ratios of DNA and collagen resulted in highly intertwined fibrous scaffolds with different fibrillar thicknesses. The formed scaffolds were biocompatible and presented as a soft matrix for cell growth and proliferation. Cells cultured on DNA/collagen scaffolds promoted the enhanced cellular uptake of transferrin, and the potential of DNA/collagen scaffolds to induce neuronal cell differentiation was further investigated. The DNA/collagen scaffolds promoted neuronal differentiation of precursor cells with extensive neurite growth in comparison to the control groups. These novel, self-assembled DNA/collagen scaffolds could serve as a platform for the development of various bioactive scaffolds with potential applications in neuroscience, drug delivery, tissue engineering, and in vitro cell culture.

Cisplatin/Apo-Transferrin Adduct: X-ray Structure and Binding to the Transferrin Receptor 1

Here, we report the X-ray structure of the adduct formed upon reaction of cisplatin, one of the most prescribed anticancer agents for the clinic treatment of solid tumors, with the apo-form of human serum transferrin (hTF). Two Pt binding sites were identified in both molecules of the adduct present in the crystal asymmetric unit: Pt binds close to the side chains of Met256 and Met499 at the N- and C-lobe, respectively. In the crystal structure, the cisplatin moiety bound to Met256 also interacts with Ser616 from a symmetry related molecule. Structural analyses, together with in solution data, demonstrate that the presence of iron does not affect the ability of hTF to bind cisplatin and that the cisplatin binding does not significantly alter the overall conformation of the different forms of the protein that remain able to form a complex with the transferrin receptor 1 (TfR1). These data suggest that the different hTF forms can be used as nanocarriers for targeted (combined) metallodrug delivery.

Quantitative analysis of transferrin uptake into living cells at single-molecule level

Endocytosis, apart from providing a mechanism for cells to take up nutrients, is the principal route of entry for many nanomedicines. The evaluation of therapeutic delivery efficiency without providing quantitative parameters, like the number of molecules entering the cell and the time of their entry, is very limited. Despite advances in single-molecule methods for in-cell quantitative measurements, they have not become widely used in the study of endocytosis. Their application, however, is challenging owing to the appropriate experimental design and applicable analysis methods. Here, by using an integrated approach based on the multidimensional time-correlated single-photon counting (TCSPC) technique, we demonstrate the quantitative method to measure the time- and concentration-dependent uptake of TRITC-transferrin into living cells with single-molecule sensitivity. The methodology opens possibilities for quantitatively assessing the delivery efficiency of fluorescent molecules into living cells.

Virus-induced vesicular acidification enhances HIV immune evasion

To inhibit endocytic entry of some viruses, cells promote acidification of endosomes by expressing the short isoform of human nuclear receptor 7 (NCOA7) which increases activity of vacuolar ATPase (V-ATPase). While we found that HIV-1 infection of primary T cells led to acidification of endosomes, NCOA7 levels were only marginally affected. Contrastingly, levels of the 50 kDa form of the sodium/hydrogen exchanger 6 (NHE6) were greatly reduced. NHE6 overexpression and low concentrations of the V-ATPase inhibitor, concanamycin A, selectively reversed endosomal acidification. Endosomal neutralization by these interventions also reduced Nef-dependent MHC-I downmodulation by our wildtype HIV reporter virus. NHE6 overexpression disrupted MHC-I downmodulation by reducing recruitment of Nef to Rab11+ compartments and inhibiting interactions between Nef, β-COP, and ARF-1. In addition, we found that the HIV Vif protein was required for downmodulation of the 50 kDa form of NHE6 and for endosomal acidification but was dispensable for Nef-dependent MHC-I downmodulation.

Second-Generation Antipsychotics Induce Metabolic Disruption in Adipose Tissue-Derived Mesenchymal Stem Cells Through an aPKC-Dependent Pathway

Metabolic syndrome (MetS) is a cluster of metabolic abnormalities, including visceral obesity, dyslipidemia, and insulin resistance. In this regard, visceral white adipose tissue (vWAT) plays a critical role, influencing energy metabolism, immunomodulation, and oxidative stress. Adipose-derived stem cells (ADSCs) are key players in these processes within vWAT. While second-generation antipsychotics (SGAs) have significantly improved treatments for mental health disorders, their chronic use is associated with an increased risk of MetS. In this study, we explored the impact of SGAs on ADSCs to better understand their role in MetS and identify potential therapeutic targets. Our findings reveal that olanzapine disrupts lipid droplet formation during adipogenic differentiation, impairing insulin receptor endocytosis, turnover, and signaling. SGAs also alter the endolysosomal compartment, leading to acidic vesicle accumulation and increased lysosomal biogenesis through TFEB activation. PKCζ is crucial for the SGA-induced nuclear translocation of TFEB and acidic vesicle formation. Notably, inhibiting PKCζ restored insulin receptor tyrosine phosphorylation, normalized receptor turnover, and improved downstream signaling following olanzapine treatment. This activation of PKCζ by olanzapine is driven by increased phosphatidic acid synthesis via phospholipase D (PLD), following G protein-coupled receptor (GPCR) signaling activation. Overall, olanzapine and clozapine disrupt endolysosomal homeostasis and insulin signaling in a PKCζ-dependent manner. These findings highlight SGAs as valuable tools for uncovering cellular dysfunction in vWAT during MetS and may guide the development of new therapeutic strategies to mitigate the metabolic side effects of these drugs.

A conserved interaction between the effector Sca4 and host clathrin suggests additional contributions for Sca4 during rickettsial infection

Intracellular bacterial pathogens deploy secreted effector proteins that manipulate diverse host machinery and pathways to promote infection. Although many effectors carry out a single function or interaction, there are a growing number of secreted effectors capable of interacting with multiple host factors. However, few effectors secreted by arthropod-borne obligate intracellular Rickettsia species have been linked to multiple host targets. Here, we investigated the conserved rickettsial secreted effector Sca4, which was previously shown to interact with host vinculin in donor cells to promote cell-to-cell spread in the model Rickettsia species R. parkeri. We discovered that Sca4 also binds the host cell protein clathrin heavy chain (CHC, CLTC) via a conserved segment in the Sca4 N-terminus. In mammalian host cells, ablation of CLTC expression or chemical inhibition of endocytosis reduced R. parkeri cell-to-cell spread, indicating that clathrin promotes efficient spread. Unexpectedly, the contribution of CHC to spread was independent of Sca4 and appeared restricted to the recipient host cell, suggesting that the Sca4-clathrin interaction regulates another aspect of the infectious lifecycle. Indeed, R. parkeri lacking Sca4 or expressing a Sca4 truncation unable to bind clathrin had markedly reduced burdens in tick cells, hinting at a cell type-specific function for the Sca4-clathrin interaction. Sca4 homologs from diverse Rickettsia species also bound clathrin, suggesting that the function of this novel effector-host interaction may be broadly important for rickettsial infection. We conclude that Sca4 has multiple targets during infection and that rickettsiae may manipulate host endocytic machinery to facilitate several stages of their life cycles.

Enzyme-Regulated Non-Thermal Fluctuations Enhance Ligand Diffusion and Receptor-Mediated Endocytosis

Active enzymes during catalyzing chemical reactions, have been found to generate significant mechanical fluctuations, which can influence the dynamics of their surroundings. These phenomena open new avenues for controlling mass transport in complex and dynamically inhomogeneous environments through localized chemical reactions. To explore this potential, we studied the uptake of transferrin molecules in retinal pigment epithelium (RPE) cells via clathrin-mediated endocytosis. In the presence of enzyme catalysis in the extracellular matrix, we observed a significant enhancement in the transport of fluorophore-tagged transferrin inside the cells. Fluorescence correlation spectroscopy measurements showed substantial increase in transferrin diffusion in the presence of active fluctuations. This study sheds light on the possibility that enzyme-substrate reactions within the extracellular matrix may induce long-range mechanical influences, facilitating targeted material delivery within intracellular milieu more efficiently than passive diffusion. These insights are expected to contribute to the development of better therapeutic strategies by overcoming limitations imposed by slow molecular diffusion under complex environments.

Cell polarity proteins promote macropinocytosis in response to metabolic stress

Macropinocytosis has emerged as a scavenging pathway that cancer cells exploit to survive in a nutrient-deprived microenvironment. Tumor cells are especially reliant on glutamine for their survival, and in pancreatic ductal adenocarcinoma (PDAC) cells, glutamine deficiency can enhance the stimulation of macropinocytosis. Here, we identify the atypical protein kinase C (aPKC) enzymes, PKCζ and PKCι, as regulators of macropinocytosis. In normal epithelial cells, aPKCs associate with the scaffold proteins Par3 and Par6 to regulate cell polarity, affecting several targets, including the Par1 kinases and we find that each of these proteins is required for macropinocytosis. Mechanistically, aPKCs are regulated by EGFR signaling or by the transcription factor CREM to promote the Par3 relocation to microtubules, facilitating macropinocytosis in a dynein-dependent manner. Importantly, cell fitness impairment caused by aPKC depletion is rescued by the restoration of macropinocytosis and aPKCs support PDAC growth in vivo. Our findings enhance our understanding of the mechanistic underpinnings that control macropinocytic uptake in the context of metabolic stress.

Sprouty2 Regulates Endocytosis and Degradation of Fibroblast Growth Factor Receptor 1 in Glioblastoma Cells

The Sprouty (SPRY) proteins are evolutionary conserved modulators of receptor tyrosine kinase (RTK) signaling. SPRY2 inhibits fibroblast growth factor (FGF) signaling, whereas it enhances epidermal growth factor (EGF) signaling through inhibition of EGF receptor (EGFR) endocytosis, ubiquitination, and degradation. In this study, we analyzed the effects of SPRY2 on endocytosis and degradation of FGF receptor 1 (FGFR1) using two human glioblastoma (GBM) cell lines with different endogenous SPRY2 levels. SPRY2 overexpression (SPRY2-OE) inhibited clathrin- and caveolae-mediated endocytosis of FGFR1, reduced the number of caveolin-1 vesicles and the uptake of transferrin. Furthermore, FGFR1 protein was decreased by SPRY2-OE, whereas EGFR protein was increased. SPRY2-OE enhanced FGFR1 degradation by increased c-casitas b-lineage lymphoma (c-CBL)-mediated ubiquitination, but it diminished binding of phospholipase Cγ1 (PLCγ1) to FGFR1. Consequently, SPRY2-OE inhibited FGF2-induced activation of PLCγ1, whereas it enhanced EGF-induced PLCγ1 activation. Despite the reduction of FGFR1 protein and the inhibition of FGF signaling, SPRY2-OE increased cell viability, and knockdown of SPRY2 enhanced the sensitivity to cisplatin. These results demonstrate that the inhibitory effect of SPRY2-OE on FGF signaling is at least in part due to the reduction in FGFR1 levels and the decreased binding of PLCγ1 to the receptor.

Ironing Out the Mechanism of gp130 Signaling

gp130 functions as a shared signal-transducing subunit not only for interleukin (IL)-6 but also for eight other human cytokine receptor complexes. The IL-6 signaling pathway mediated through gp130 encompasses classical, trans, or cluster signaling, intricately regulated by a diverse array of modulators affecting IL-6, its receptor, and gp130. Currently, only a limited number of small molecule antagonists and agonists for gp130 are known. This review aims to comprehensively examine the current knowledge of these modulators and provide insights into their pharmacological properties, particularly in the context of cancer and other diseases. Notably, the prominent gp130 modulators SC144, bazedoxifene, and raloxifene are discussed in detail, with a specific focus on the discovery of SC144's iron-chelating properties. This adds a new dimension to the understanding of its pharmacological effects and therapeutic potential in conditions where iron homeostasis is significant. Our bioinformatic analysis of gp130 and genes related to iron homeostasis reveals insightful correlations, implicating the role of iron in the gp130 signaling pathway. Overall, this review contributes to the evolving understanding of gp130 modulation and its potential therapeutic applications in various disease contexts. SIGNIFICANCE STATEMENT: This perspective provides a timely and comprehensive analysis of advancements in gp130 signaling research, emphasizing the therapeutic implications of the currently available modulators. Bioinformatic analysis demonstrates potential interplay between gp130 and genes that regulate iron homeostasis, suggesting new therapeutic avenues. By combining original research findings with a broader discussion of gp130's therapeutic potential, this perspective significantly contributes to the field.

Hypothalamic tanycytes internalize ghrelin from the cerebrospinal fluid: Molecular mechanisms and functional implications

OBJECTIVE

The peptide hormone ghrelin exerts potent effects in the brain, where its receptor is highly expressed. Here, we investigated the role of hypothalamic tanycytes in transporting ghrelin across the blood-cerebrospinal fluid (CSF) interface.

METHODS

We investigated the internalization and transport of fluorescent ghrelin (Fr-ghrelin) in primary cultures of rat hypothalamic tanycytes, mouse hypothalamic explants, and mice. We also tested the impact of inhibiting clathrin-mediated endocytosis of ghrelin in the brain ventricular system on the orexigenic and locomotor effects of the hormone.

RESULTS

In vitro, we found that Fr-ghrelin is selectively and rapidly internalized at the soma of tanycytes, via a GHSR-independent and clathrin-dependent mechanism, and then transported to the endfoot. In hypothalamic explants, we also found that Fr-ghrelin is internalized at the apical pole of tanycytes. In mice, Fr-ghrelin present in the CSF was rapidly internalized by hypothalamic β-type tanycytes in a clathrin-dependent manner, and pharmacological inhibition of clathrin-mediated endocytosis in the brain ventricular system prolonged the ghrelin-induced locomotor effects.

CONCLUSIONS

We propose that tanycyte-mediated transport of ghrelin is functionally relevant, as it may contribute to reduce the concentration of this peptide hormone in the CSF and consequently shortens the duration of its central effects.

CYpHER: catalytic extracellular targeted protein degradation with high potency and durable effect

Many disease-causing proteins have multiple pathogenic mechanisms, and conventional inhibitors struggle to reliably disrupt more than one. Targeted protein degradation (TPD) can eliminate the protein, and thus all its functions, by directing a cell's protein turnover machinery towards it. Two established strategies either engage catalytic E3 ligases or drive uptake towards the endolysosomal pathway. Here we describe CYpHER (CatalYtic pH-dependent Endolysosomal delivery with Recycling) technology with potency and durability from a catalytic mechanism that shares the specificity and straightforward modular design of endolysosomal uptake. By bestowing pH-dependent release on the target engager and using the rapid-cycling transferrin receptor as the uptake receptor, CYpHER induces endolysosomal delivery of surface and extracellular targets while re-using drug, potentially yielding increased potency and reduced off-target tissue exposure risks. The TfR-based approach allows targeting to tumors that overexpress this receptor and offers the potential for transport to the CNS. CYpHER function was demonstrated in vitro with EGFR and PD-L1, and in vivo with EGFR in a model of EGFR-driven non-small cell lung cancer.

Impaired endocytosis and accumulation in early endosomal compartments defines herpes simplex virus-mediated disruption of the nonclassical MHC class I-related molecule MR1

Presentation of metabolites by the major histocompatibility complex class I-related protein 1 (MR1) molecule to mucosal-associated invariant T cells is impaired during herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) infections. This is surprising given these viruses do not directly synthesise MR1 ligands. We have previously identified several HSV proteins responsible for rapidly downregulating the intracellular pool of immature MR1, effectively inhibiting new surface antigen presentation, while preexisting ligand-bound mature MR1 is unexpectedly upregulated by HSV-1. Using flow cytometry, immunoblotting, and high-throughput fluorescence microscopy, we demonstrate that the endocytosis of surface MR1 is impaired during HSV infection and that internalized molecules accumulate in EEA1-labeled early endosomes, avoiding degradation. We establish that the short MR1 cytoplasmic tail is not required for HSV-1-mediated downregulation of immature molecules; however it may play a role in the retention of mature molecules on the surface and in early endosomes. We also determine that the HSV-1 US3 protein, the shorter US3.5 kinase and the full-length HSV-2 homolog, all predominantly target mature surface rather than total MR1 levels. We propose that the downregulation of intracellular and cell surface MR1 molecules by US3 and other HSV proteins is an immune-evasive countermeasure to minimize the effect of impaired MR1 endocytosis, which might otherwise render infected cells susceptible to MR1-mediated killing by mucosal-associated invariant T cells.

CHC22 clathrin recruitment to the early secretory pathway requires two-site interaction with SNX5 and p115

The two clathrin isoforms, CHC17 and CHC22, mediate separate intracellular transport routes. CHC17 performs endocytosis and housekeeping membrane traffic in all cells. CHC22, expressed most highly in skeletal muscle, shuttles the glucose transporter GLUT4 from the ERGIC (endoplasmic-reticulum-to-Golgi intermediate compartment) directly to an intracellular GLUT4 storage compartment (GSC), from where GLUT4 can be mobilized to the plasma membrane by insulin. Here, molecular determinants distinguishing CHC22 from CHC17 trafficking are defined. We show that the C-terminal trimerization domain of CHC22 interacts with SNX5, which also binds the ERGIC tether p115. SNX5, and the functionally redundant SNX6, are required for CHC22 localization independently of their participation in the endosomal ESCPE-1 complex. In tandem, an isoform-specific patch in the CHC22 N-terminal domain separately mediates binding to p115. This dual mode of clathrin recruitment, involving interactions at both N- and C-termini of the heavy chain, is required for CHC22 targeting to ERGIC membranes to mediate the Golgi-bypass route for GLUT4 trafficking. Interference with either interaction inhibits GLUT4 targeting to the GSC, defining a bipartite mechanism regulating a key pathway in human glucose metabolism.

Lysosomal physiology and pancreatic lysosomal stress in diabetes mellitus

Endocrine and exocrine functions of the pancreas control nutritional absorption, utilisation and systemic metabolic homeostasis. Under basal conditions, the lysosome is pivotal in regulating intracellular organelles and metabolite turnover. In response to acute or chronic stress, the lysosome senses metabolic flux and inflammatory challenges, thereby initiating the adaptive programme to re-establish cellular homeostasis. A growing body of evidence has demonstrated the pathophysiological relevance of the lysosomal stress response in metabolic diseases in diverse sets of tissues/organs, such as the liver and the heart. In this review, we discuss the pathological relevance of pancreatic lysosome stress in diabetes mellitus. We begin by summarising lysosomal biology, followed by exploring the immune and metabolic functions of lysosomes and finally discussing the interplay between lysosomal stress and the pathogenesis of pancreatic diseases. Ultimately, our review aims to enhance our understanding of lysosomal stress in disease pathogenesis, which could potentially lead to the discovery of innovative treatment methods for these conditions.

Membrane trafficking of synaptic adhesion molecules

Synapse formation and stabilization are aided by several families of adhesion molecules, which are generally seen as specialized surface receptors. The function of most surface receptors, including adhesion molecules, is modulated in non-neuronal cells by the processes of endocytosis and recycling, which control the number of active receptors found on the cell surface. These processes have not been investigated extensively at the synapse. This review focuses on the current status of this topic, summarizing general findings on the membrane trafficking of the most prominent synaptic adhesion molecules. Remarkably, evidence for endocytosis processes has been obtained for many synaptic adhesion proteins, including dystroglycans, latrophilins, calsyntenins, netrins, teneurins, neurexins, neuroligins and neuronal pentraxins. Less evidence has been obtained on their recycling, possibly because of the lack of specific assays. We conclude that the trafficking of the synaptic adhesion molecules is an important topic, which should receive more attention in the future.

Secondary Envelopment of Human Cytomegalovirus Is a Fast Process Utilizing the Endocytic Compartment as a Major Membrane Source

Secondary envelopment of the human cytomegalovirus (HCMV) is a critical but not well-understood process that takes place at the cytoplasmic viral assembly complex (cVAC) where nucleocapsids acquire their envelope by budding into cellular membranes containing viral glycoproteins. Previous studies presented controversial results regarding the composition of the viral envelope, suggesting trans-Golgi and endosomal origins, as well as intersections with the exosomal and endocytic pathways. Here, we investigated the role of endocytic membranes for the secondary envelopment of HCMV by using wheat germ agglutinin (WGA) pulse labeling to label glycoproteins at the plasma membrane and to follow their trafficking during HCMV infection by light microscopy and transmission electron microscopy (TEM). WGA labeled different membrane compartments within the cVAC, including early endosomes, multivesicular bodies, trans-Golgi, and recycling endosomes. Furthermore, TEM analysis showed that almost 90% of capsids undergoing secondary envelopment and 50% of enveloped capsids were WGA-positive within 90 min. Our data reveal extensive remodeling of the endocytic compartment in the late stage of HCMV infection, where the endocytic compartment provides an optimized environment for virion morphogenesis and serves as the primary membrane source for secondary envelopment. Furthermore, we show that secondary envelopment is a rapid process in which endocytosed membranes are transported from the plasma membrane to the cVAC within minutes to be utilized by capsids for envelopment.

Dual Chemotherapeutic Loading in Oxalate Transferrin-Conjugated Polymersomes Incorporated into Chitosan Hydrogels for Site-Specific Targeting of Melanoma Cells

In this work, we developed a smart drug delivery system composed of poly (ethylene glycol)-block-poly (ε-caprolactone) (PEG-PCL)-based polymersomes (Ps) loaded with doxorubicin (DOX) and vemurafenib (VEM). To enhance targeted delivery to malignant melanoma cells, these drug-loaded nanovesicles were conjugated to the oxalate transferrin variant (oxalate Tf) and incorporated into three-dimensional chitosan hydrogels. This innovative approach represents the first application of oxalate Tf for the precision delivery of drug-loaded polymersomes within a semi-solid dosage form based on chitosan hydrogels. These resulting semi-solids exhibited a sustained release profile for both encapsulated drugs. To evaluate their potency, we compared the cytotoxicity of native Tf-Ps with oxalate Tf-Ps. Notably, the oxalate Tf-Ps demonstrated a 3-fold decrease in cell viability against melanoma cells compared to normal cells and were 1.6-fold more potent than native Tf-Ps, indicating the greater potency of this nanoformulation. These findings suggest that dual-drug delivery using an oxalate-Tf-targeting ligand significantly enhances the drug delivery efficiency of Tf-conjugated nanovesicles and offers a promising strategy to overcome the challenge of multidrug resistance in melanoma therapy.

A Novel Fluorescent Gemcitabine Prodrug That Follows a Nucleoside Transporter-Independent Internalization and Bears Enhanced Therapeutic Efficacy With Respect to Gemcitabine

The multiplexity of cancer has rendered it the second leading cause of mortality worldwide and theragnostic prodrugs have gained popularity in recent years as a means of treatment. Theragnostic prodrugs enable the simultaneous diagnosis and therapy of tumors via high-precision real-time drug release monitoring. Herein, we report the development of the small theragnostic prodrug GF, based on the nucleoside anticancer agent gemcitabine and the fluorescent dye 5(6)-carboxyfluorescein. We have successfully demonstrated its efficient internalization in tumor cells, showing localization throughout both the early and late endocytic pathways. Its mechanism of cell internalization was evaluated, confirming its independence from nucleoside transporters. Its cellular localization via confocal microscopy revealed a clathrin-mediated endocytosis mechanism, distinguishing it from analogous compounds studied previously. Furthermore, GF exhibited stability across various pH values and in human blood plasma. Subsequently, its in vitro cytotoxicity was assessed in three human cancer cell lines (A549, U87 and T98). Additionally, its pharmacokinetic profile in mice was investigated and the consequent drug release was monitored. Finally, its in vivo visualization was accomplished in zebrafish xenotransplantation models and its in vivo efficacy was evaluated in A549 xenografts. The results unveiled an intriguing efficacy profile, positioning GF as a compelling candidate warranting further investigation.

Ubiquitin-driven protein condensation stabilizes clathrin-mediated endocytosis

Clathrin-mediated endocytosis is an essential cellular pathway that enables signaling and recycling of transmembrane proteins and lipids. During endocytosis, dozens of cytosolic proteins come together at the plasma membrane, assembling into a highly interconnected network that drives endocytic vesicle biogenesis. Recently, multiple groups have reported that early endocytic proteins form flexible condensates, which provide a platform for efficient assembly of endocytic vesicles. Given the importance of this network in the dynamics of endocytosis, how might cells regulate its stability? Many receptors and endocytic proteins are ubiquitylated, while early endocytic proteins such as Eps15 contain ubiquitin-interacting motifs. Therefore, we examined the influence of ubiquitin on the stability of the early endocytic protein network. In vitro, we found that recruitment of small amounts of polyubiquitin dramatically increased the stability of Eps15 condensates, suggesting that ubiquitylation could nucleate endocytic assemblies. In live-cell imaging experiments, a version of Eps15 that lacked the ubiquitin-interacting motif failed to rescue defects in endocytic initiation created by Eps15 knockout. Furthermore, fusion of Eps15 to a deubiquitylase enzyme destabilized nascent endocytic sites within minutes. In both in vitro and live-cell settings, dynamic exchange of Eps15 proteins, a measure of protein network stability, was decreased by Eps15-ubiquitin interactions and increased by loss of ubiquitin. These results collectively suggest that ubiquitylation drives assembly of the flexible protein network responsible for catalyzing endocytic events. More broadly, this work illustrates a biophysical mechanism by which ubiquitylated transmembrane proteins at the plasma membrane could regulate the efficiency of endocytic internalization.

ARF4-mediated retrograde trafficking as a driver of chemoresistance in glioblastoma

BACKGROUND

Cellular functions hinge on the meticulous orchestration of protein transport, both spatially and temporally. Central to this process is retrograde trafficking, responsible for targeting proteins to the nucleus. Despite its link to many diseases, the implications of retrograde trafficking in glioblastoma (GBM) are still unclear.

METHODS

To identify genetic drivers of TMZ resistance, we conducted comprehensive CRISPR-knockout screening, revealing ADP-ribosylation factor 4 (ARF4), a regulator of retrograde trafficking, as a major contributor.

RESULTS

Suppressing ARF4 significantly enhanced TMZ sensitivity in GBM patient-derived xenograft (PDX) models, leading to improved survival rates (P < .01) in both primary and recurrent lines. We also observed that TMZ exposure stimulates ARF4-mediated retrograde trafficking. Proteomics analysis of GBM cells with varying levels of ARF4 unveiled the influence of this pathway on EGFR signaling, with increased nuclear trafficking of EGFR observed in cells with ARF4 overexpression and TMZ treatment. Additionally, spatially resolved RNA-sequencing of GBM patient tissues revealed substantial correlations between ARF4 and crucial nuclear EGFR (nEGFR) downstream targets, such as MYC, STAT1, and DNA-PK. Decreased activity of DNA-PK, a DNA repair protein downstream of nEGFR signaling that contributes to TMZ resistance, was observed in cells with suppressed ARF4 levels. Notably, treatment with DNA-PK inhibitor, KU-57788, in mice with a recurrent PDX line resulted in prolonged survival (P < .01), highlighting the promising therapeutic implications of targeting proteins reliant on ARF4-mediated retrograde trafficking.

CONCLUSIONS

Our findings demonstrate that ARF4-mediated retrograde trafficking contributes to the development of TMZ resistance, cementing this pathway as a viable strategy to overcome chemoresistance in GBM.

Novel selective inhibitors of macropinocytosis-dependent growth in pancreatic ductal carcinoma

Macropinocytosis is a cellular process that enables cells to engulf extracellular material, such as nutrients, growth factors, and even whole cells. It is involved in several physiological functions as well as pathological conditions. In cancer cells, macropinocytosis plays a crucial role in promoting tumor growth and survival under nutrient-limited conditions. In particular KRAS mutations have been identified as main drivers of macropinocytosis in pancreatic, breast, and non-small cell lung cancers. We performed a high-content screening to identify inhibitors of macropinocytosis in pancreatic ductal adenocarcinoma (PDAC)-derived cells, aiming to prevent nutrient scavenging of PDAC tumors. The screening campaign was conducted in a well-known pancreatic KRAS-mutated cell line (MIAPaCa-2) cultured under nutrient deprivation and using FITC-dextran to precisely quantify macropinocytosis. We assembled a collection of 3584 small molecules, including drugs approved by the Food and Drug Administration (FDA), drug-like molecules against molecular targets, kinase-targeted compounds, and molecules designed to hamper protein-protein interactions. We identified 28 molecules that inhibited macropinocytosis, with potency ranging from 0.4 to 29.9 μM (EC50). A few of them interfered with other endocytic pathways, while 11 compounds did not and were therefore considered specific "bona fide" macropinocytosis inhibitors and further characterized. Four compounds (Ivermectin, Tyrphostin A9, LY2090314, and Pyrvinium Pamoate) selectively hampered nutrient scavenging in KRAS-mutated cancer cells. Their ability to impair albumin-dependent proliferation was replicated both in different 2D cell culture systems and 3D organotypic models. These findings provide a new set of compounds specifically targeting macropinocytosis, which could have therapeutic applications in cancer and infectious diseases.

Circulating low-molecular-weight (poly)phenol metabolites in the brain: unveiling in vitro and in vivo blood-brain barrier transport

Circulating metabolites resulting from colonic metabolism of dietary (poly)phenols are highly abundant in the bloodstream, though still marginally explored, particularly concerning their brain accessibility. Our goal is to disclose (poly)phenol metabolites' blood-brain barrier (BBB) transport, in vivo and in vitro, as well as their role at BBB level. For three selected metabolites, benzene-1,2-diol-3-sulfate/benzene-1,3-diol-2-sulfate (pyrogallol-sulfate - Pyr-sulf), benzene-1,3-diol-6-sulfate (phloroglucinol-sulfate - Phlo-sulf), and phenol-3-sulfate (resorcinol-sulfate - Res-sulf), BBB transport was assessed in human brain microvascular endothelial cells (HBMEC). Their potential in modulating in vitro BBB properties at circulating concentrations was also studied. Metabolites' fate towards the brain, liver, kidney, urine, and blood was disclosed in Wistar rats upon injection. Transport kinetics in HBMEC highlighted different BBB permeability rates, where Pyr-sulf emerged as the most in vitro BBB permeable metabolite. Pyr-sulf was also the most potent regarding BBB properties improvement, namely increased beta(β)-catenin membrane expression and reduction of zonula occludens-1 membrane gaps. Whereas no differences were observed for transferrin, increased expression of caveolin-1 upon Pyr-sulf and Res-sulf treatments was found. Pyr-sulf was also capable of modulating gene and protein expression of some solute carrier transporters. Notably, each of the injected metabolites exhibited a unique tissue distribution in vivo, with the remarkable ability to almost immediately reach the brain.

Emergent Spatiotemporal Organization in Stochastic Intracellular Transport Dynamics

The interior of a living cell is an active, fluctuating, and crowded environment, yet it maintains a high level of coherent organization. This dichotomy is readily apparent in the intracellular transport system of the cell. Membrane-bound compartments called endosomes play a key role in carrying cargo, in conjunction with myriad components including cargo adaptor proteins, membrane sculptors, motor proteins, and the cytoskeleton. These components coordinate to effectively navigate the crowded cell interior and transport cargo to specific intracellular locations, even though the underlying protein interactions and enzymatic reactions exhibit stochastic behavior. A major challenge is to measure, analyze, and understand how, despite the inherent stochasticity of the constituent processes, the collective outcomes show an emergent spatiotemporal order that is precise and robust. This review focuses on this intriguing dichotomy, providing insights into the known mechanisms of noise suppression and noise utilization in intracellular transport processes, and also identifies opportunities for future inquiry.

How are Trypanosoma brucei receptors protected from host antibody-mediated attack?

Trypanosoma brucei is the causal agent of African Trypanosomiasis in humans and other animals. It maintains a long-term infection through an antigenic variation based population survival strategy. To proliferate in a mammal, T. brucei acquires iron and haem through the receptor mediated uptake of host transferrin and haptoglobin-hemoglobin respectively. The receptors are exposed to host antibodies but this does not lead to clearance of the infection. Here we discuss how the trypanosome avoids this fate in the context of recent findings on the structure and cell biology of the receptors.

Membrane topography and the overestimation of protein clustering in single molecule localisation microscopy - identification and correction

According to single-molecule localisation microscopy almost all plasma membrane proteins are clustered. We demonstrate that clusters can arise from variations in membrane topography where the local density of a randomly distributed membrane molecule to a degree matches the variations in the local amount of membrane. Further, we demonstrate that this false clustering can be differentiated from genuine clustering by using a membrane marker to report on local variations in the amount of membrane. In dual colour live cell single molecule localisation microscopy using the membrane probe DiI alongside either the transferrin receptor or the GPI-anchored protein CD59, we found that pair correlation analysis reported both proteins and DiI as being clustered, as did its derivative pair correlation-photoactivation localisation microscopy and nearest neighbour analyses. After converting the localisations into images and using the DiI image to factor out topography variations, no CD59 clusters were visible, suggesting that the clustering reported by the other methods is an artefact. However, the TfR clusters persisted after topography variations were factored out. We demonstrate that membrane topography variations can make membrane molecules appear clustered and present a straightforward remedy suitable as the first step in the cluster analysis pipeline.

A conserved interaction between the effector Sca4 and host endocytic machinery suggests additional roles for Sca4 during rickettsial infection

Intracellular bacterial pathogens deploy secreted effector proteins that manipulate diverse host machinery and pathways to promote infection. Although many effectors carry out a single specific function or interaction, there are a growing number of secreted pathogen effectors capable of interacting with multiple host factors. However, few effectors secreted by obligate intracellular Rickettsia species have been linked to multiple host targets. Here, we investigated the conserved rickettsial secreted effector Sca4, which was previously shown to interact with host vinculin to promote cell-to-cell spread in the model Rickettsia species R. parkeri . We discovered that Sca4 also binds the host cell endocytic factor clathrin heavy chain (CHC, CLTC ) via a conserved segment in the Sca4 N-terminus. Ablation of CLTC expression or chemical inhibition of endocytosis reduced R. parkeri cell-to-cell spread, indicating that clathrin promotes efficient spread between mammalian cells. This activity was independent of Sca4 and appeared restricted to the recipient host cell, suggesting that the Sca4-clathrin interaction also regulates another aspect of the infectious lifecycle. Indeed, R. parkeri lacking Sca4 or expressing a Sca4 truncation unable to bind clathrin had markedly reduced burdens in tick cells, hinting at a cell-type specific function for the Sca4-clathrin interaction. Sca4 homologs from diverse Rickettsia species also bound clathrin, suggesting that the function of this novel effector-host interaction may be broadly important for rickettsial infection. We conclude that Sca4 has multiple targets during infection and that rickettsiae may manipulate host endocytic machinery to facilitate several stages of their life cycles.

Comparing Cell Penetration of Biotherapeutics across Human Cell Lines

A major obstacle in biotherapeutics development is maximizing cell penetration. Ideally, assays would allow for optimization of cell penetration in the cell type of interest early in the drug development process. However, few assays exist to compare cell penetration across different cell types independent of drug function. In this work, we applied the chloroalkane penetration assay (CAPA) in seven mammalian cell lines as well as primary cells. Careful controls were used to ensure that data could be compared across cell lines. We compared the nuclear penetration of several peptides and drug-like oligonucleotides and saw significant differences among the cell lines. To help explain these differences, we quantified the relative activities of endocytosis pathways in these cell lines and correlated them with the penetration data. Based on these results, we knocked down clathrin in a cell line with an efficient permeability profile and observed reduced penetration of peptides but not oligonucleotides. Finally, we used small-molecule endosomal escape enhancers and observed enhancement of cell penetration of some oligonucleotides, but only in some of the cell lines tested. CAPA data provide valuable points of comparison among different cell lines, including primary cells, for evaluating the cell penetration of various classes of peptides and oligonucleotides.

Residence of the Nucleotide Sugar Transporter Family Members SLC35F1 and SLC35F6 in the Endosomal/Lysosomal Pathway

The SLC35 (Solute Carrier 35) family members acting as nucleotide sugar transporters are typically localized in the endoplasmic reticulum or Golgi apparatus. It is, therefore, intriguing that some reports document the presence of orphan transporters SLC35F1 and SLC35F6 within the endosomal and lysosomal system. Here, we compared the subcellular distribution of these proteins and found that they are concentrated in separate compartments; i.e., recycling endosomes for SLC35F1 and lysosomes for SLC35F6. Swapping the C-terminal tail of these proteins resulted in a switch of localization, with SLC35F1 being trafficked to lysosomes while SLC35F6 remained in endosomes. This suggested the presence of specific sorting signals in these C-terminal regions. Using site-directed mutagenesis, fluorescence microscopy, and cell surface biotinylation assays, we found that the EQERLL360 signal located in the cytoplasmic tail of human SLC35F6 is involved in its lysosomal sorting (as previously shown for this conserved sequence in mouse SLC35F6), and that SLC35F1 localization in the recycling pathway depends on two YXXΦ-type signals: a Y367KQF sequence facilitates its internalization from the plasma membrane, while a Y392TSL motif prevents its transport to lysosomes, likely by promoting SLC35F1 recycling to the cell surface. Taken together, these results support that some SLC35 members may function at different levels of the endosomal and lysosomal system.

Tailoring lipid nanoparticles for T-cell targeting in allergic asthma: Insights into efficacy and specificity

Asthma impacts over 300 million patients globally, with significant health implications, especially in cases of its allergic subtype. The disease is characterized by a complex interplay of airway inflammation and immune responses, often mediated by Th2 cell-related cytokines. In this study, we engineered lipid nanoparticles (LNPs) to specifically deliver therapeutic siRNA via the transferrin receptor to T cells. Strain-promoted azide-alkyne cycloaddition (SPAAC) was employed for the conjugation of transferrin ligands to PEGylated lipids in the LNPs, with the goal of enhancing cellular uptake and gene knockdown. The obtained LNPs exhibited characteristics that make them suitable for pulmonary delivery. Using methods such as nanoparticle tracking analysis (NTA) and enzyme-linked immunosorbent assay (ELISA), we determined the average number of transferrin molecules bound to individual LNPs. Additionally, we found that cellular uptake was ligand-dependent, achieving a GATA3 knockdown of more than 50% in relevant in vitro and ex vivo models. Notably, our findings highlight the limitations inherent to modifying the surface of LNPs, particularly with regard to their targeting capabilities. This work paves the way for future research aimed at optimizing targeted LNPs for the treatment of immunologic diseases such as allergic asthma.

CYpHER: Catalytic extracellular targeted protein degradation with high potency and durable effect

Many disease-causing proteins have multiple pathogenic mechanisms, and conventional inhibitors struggle to reliably disrupt more than one. Targeted protein degradation (TPD) can eliminate the protein, and thus all its functions, by directing a cell's protein turnover machinery towards it. Two established strategies either engage catalytic E3 ligases or drive uptake towards the endolysosomal pathway. Here we describe CYpHER (CatalYtic pH-dependent Endolysosomal delivery with Recycling) technology with potency and durability from a novel catalytic mechanism that shares the specificity and straightforward modular design of endolysosomal uptake. By bestowing pH-dependent release on the target engager and using the rapid-cycling transferrin receptor as the uptake receptor, CYpHER induces endolysosomal target delivery while re-using drug, potentially yielding increased potency and reduced off-target tissue exposure risks. The TfR-based approach allows targeting to tumors that overexpress this receptor and offers the potential for transport to the CNS. CYpHER function was demonstrated in vitro with EGFR and PD-L1, and in vivo with EGFR in a model of EGFR-driven non-small cell lung cancer.

Nose-to-brain selective drug delivery to glioma via ferritin-based nanovectors reduces tumor growth and improves survival rate

Gliomas are among the most fatal tumors, and the available therapeutic options are very limited. Additionally, the blood-brain barrier (BBB) prevents most drugs from entering the brain. We designed and produced a ferritin-based stimuli-sensitive nanocarrier with high biocompatibility and water solubility. It can incorporate high amounts of the potent topoisomerase 1 inhibitor Genz-644282. Here, we show that this nanocarrier, named The-0504, can cross the BBB and specifically deliver the payload to gliomas that express high amounts of the ferritin/transferrin receptor TfR1 (CD71). Intranasal or intravenous administration of The-0504 both reduce tumor growth and improve the survival rate of glioma-bearing mice. However, nose-to-brain administration is a simpler and less invasive route that may spare most of the healthy tissues compared to intravenous injections. For this reason, the data reported here could pave the way towards a new, safe, and direct ferritin-based drug delivery method for brain diseases, especially brain tumors.

Rab GTPases and phosphoinositides fine-tune SNAREs dependent targeting specificity of intracellular vesicle traffic

In the secretory pathway the destination of trafficking vesicles is determined by specific proteins that, with the notable exception of SNAREs, are recruited from soluble pools. Previously we have shown that microinjected proteoliposomes containing early or late endosomal SNAREs, respectively, are targeted to the corresponding endogenous compartments, with targeting specificity being dependent on the recruitment of tethering factors by some of the SNAREs. Here, we show that targeting of SNARE-containing liposomes is refined upon inclusion of polyphosphoinositides and Rab5. Intriguingly, targeting specificity is dependent on the concentration of PtdIns(3)P, and on the recruitment of PtdIns(3)P binding proteins such as rabenosyn-5 and PIKfyve, with conversion of PtdIns(3)P into PtdIns(3,5)P2 re-routing the liposomes towards late endosomes despite the presence of GTP-Rab5 and early endosomal SNAREs. Our data reveal a complex interplay between permissive and inhibitory targeting signals that sharpen a basic targeting and fusion machinery for conveying selectivity in intracellular membrane traffic.

Ganglioside GM3 Protects Against Abdominal Aortic Aneurysm by Suppressing Ferroptosis

BACKGROUND

Abdominal aortic aneurysm (AAA) is a potentially life-threatening vascular condition, but approved medical therapies to prevent AAA progression and rupture are currently lacking. Sphingolipid metabolism disorders are associated with the occurrence and development of AAA. It has been discovered that ganglioside GM3, a sialic acid-containing type of glycosphingolipid, plays a protective role in atherosclerosis, which is an important risk factor for AAA; however, the potential contribution of GM3 to AAA development has not been investigated.

METHODS

We performed a metabolomics study to evaluated GM3 level in plasma of human patients with AAA. We profiled GM3 synthase (ST3GAL5) expression in the mouse model of aneurysm and human AAA tissues through Western blotting and immunofluorescence staining. RNA sequencing, affinity purification and mass spectrometry, proteomic analysis, surface plasmon resonance analysis, and functional studies were used to dissect the molecular mechanism of GM3-regulating ferroptosis. We conditionally deleted and overexpressed St3gal5 in smooth muscle cells (SMCs) in vivo to investigate its role in AAA.

RESULTS

We found significantly reduced plasma levels of GM3 in human patients with AAA. GM3 content and ST3GAL5 expression were decreased in abdominal aortic vascular SMCs in patients with AAA and an AAA mouse model. RNA sequencing analysis showed that ST3GAL5 silencing in human aortic SMCs induced ferroptosis. We showed that GM3 interacted directly with the extracellular domain of TFR1 (transferrin receptor 1), a cell membrane protein critical for cellular iron uptake, and disrupted its interaction with holo-transferrin. SMC-specific St3gal5 knockout exacerbated iron accumulation at lesion sites and significantly promoted AAA development in mice, whereas GM3 supplementation suppressed lipid peroxidation, reduced iron deposition in aortic vascular SMCs, and markedly decreased AAA incidence.

CONCLUSIONS

Together, these results suggest that GM3 dysregulation promotes ferroptosis of vascular SMCs in AAA. Furthermore, GM3 may constitute a new therapeutic target for AAA.