Coordinated binding of Vps4 to ESCRT-III drives membrane neck constriction during MVB vesicle formation

RAB5 is a host dependency factor for the generation of SARS-CoV-2 replication organelles

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains a threat due to the emergence of variants with increased transmissibility and enhanced escape from immune responses. Like other coronaviruses before, SARS-CoV-2 likely emerged after its transmission from bats. The successful propagation of SARS-CoV-2 in humans might have been facilitated by usurping evolutionarily conserved cellular factors to execute crucial steps in its life cycle, such as the generation of replication organelles-membrane structures where coronaviruses assemble their replication-transcription complex. In this study, we found that RAB5, which is highly conserved across mammals, is a critical host dependency factor for the replication of the SARS-CoV-2 genome. Our results also suggest that SARS-CoV-2 uses RAB5+ membranes to build replication organelles with the aid of COPB1, a component of the COP-I complex, and that the virus protein NSP6 participates in this process. Hence, targeting NSP6 represents a promising approach to interfere with SARS-CoV-2 RNA synthesis and halt its propagation.IMPORTANCEIn this study, we sought to identify the host dependency factors that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) uses for the generation of replication organelles: cellular membranous structures that SARS-CoV-2 builds in order to support the replication and transcription of its genome. We uncovered that RAB5 is an important dependency factor for SARS-CoV-2 replication and the generation of replication organelles, and that the viral protein NSP6 participates in this process. Hence, NSP6 represents a promising target to halt SARS-CoV-2 replication.

Protocol for HIV-1 budding control by inducible inhibition of ESCRT-III

We present a protocol for temporal inhibition of HIV-1 virus-like particle (VLP) release using ESCRT-III proteins fused to the Hepatitis C virus NS3 protease. These fusion proteins function like wild-type ESCRT-III but convert into dominant-negative inhibitors upon addition of the NS3 inhibitor Glecaprevir. The procedure involves co-transfection of Gag and CHMP-NS3-Green plasmids into HEK293 or HeLa cells, followed by drug treatment. Steps for protein expression analysis, VLP quantification by immunoblotting, and live-cell imaging of VLP release kinetics are included. For complete details on the use and execution of this protocol, please refer to Wang et al.1.

Induced cuproptosis by targeting the ESCRT-III complex potentiates copper-based control of smut diseases

Sporisorium scitamineum, the fungal pathogen causing sugarcane smut, employs a unique copper detoxification mechanism to evade cuproptosis, a copper-dependent cell death pathway recently highlighted in anticancer research. This study reveals its copper tolerance through a novel cuproptosis evasion strategy. Through fluorescence tracing of the SsCtr3 transporter and copper ions combined with elesclomol induction, we found that the ESCRT pathway mediates SsCtr3 to sequester excess copper into vacuoles under high‑copper stress. This sequestration prevents cytoplasmic copper overload and subsequent mitochondrial DLAT aggregation that triggers cuproptosis. Pathogenicity assays revealed that disrupting the ESCRT pathway significantly enhances efficacy of copper-based compounds treatments. By elucidating the molecular crosstalk between fungal copper transport and cuproptosis suppression, this study delineates the fungus's copper homeostasis-cuproptosis axis, providing a strategic framework for optimizing copper-based disease control in sugarcane and related crops.

Classical swine fever virus recruits ALIX and ESCRT-III to facilitate viral budding

Classical swine fever virus (CSFV) incurs substantial economic losses in the global swine industry due to its persistent emergence and re-emergence across various countries. However, the precise mechanisms governing CSFV budding remain inadequately understood. Our study elucidates that the endosomal sorting complex required for transport (ESCRT)-associated protein ALIX, in conjunction with ESCRT-III, plays a pivotal role in orchestrating CSFV budding. Genomic sequence analysis identified a critical interaction between the YPXnL late domain on the E2 protein and ALIX. Through immunoprecipitation and structural domain deletion assays, we demonstrated that the ALIX Bro1 domain specifically recognized viral particles by binding to the YPXnL motif. Immunoelectron and transmission electron microscopy further confirmed that, upon infection, ALIX accumulated at the periphery of subcellular organelles, including COPII vesicles, endosomes, and the Golgi apparatus, thereby facilitating CSFV budding. Our findings also revealed that ESCRT-III subunits CHMP2B, CHMP4B, CHMP7, and VPS4A interacted with ALIX to expedite CSFV budding. Notably, Rab8 activated by Kif4A contributed to the release of CSFV particles by interacting with ALIX and directing ALIX-containing vesicles along microtubules toward the cytosol. Our study demonstrates that ALIX specifically recognizes E2 and orchestrates the recruitment of ESCRT-III and Rab8 to facilitate the vesicular budding of CSFV particles from the Golgi apparatus to the cytosol. Ultimately, virus-laden vesicles propelled by Kif4A are transported along microtubules to the plasma membrane for release. Our findings offer the first comprehensive elucidation of the CSFV budding process and contribute to the identification of antiviral targets, thereby advancing the development of antiviral therapeutics.IMPORTANCEThe endosomal sorting complex required for transport (ESCRT) machinery plays a pivotal role in the sorting of membrane proteins in eukaryotic cells and regulating various stages of infection for numerous viruses. Previous studies have underscored the indispensable role of ESCRT in the cellular entry and replication of classical swine fever virus (CSFV). However, the precise mechanisms by which ESCRT recognizes CSFV particles and initiates viral vesicle budding have remained elusive. This study reveals that the Bro1 domain of ALIX initiates viral budding proximal to the Golgi apparatus by specifically recognizing the YPXnL late domain on the CSFV E2 protein. Mechanistically, ALIX and ESCRT-III facilitate Rab8-regulated endosomal transport of CSFV particles from the Golgi apparatus to the plasma membrane. Subsequently, virions are propelled by the kinesin Kif4A along microtubules for egress into the extracellular space. In summary, these findings significantly advance our understanding of CSFV pathogenesis and offer valuable insights into the vesicular transport and budding mechanisms of CSFV particles.

Recent Progress in Developing Extracellular Vesicles as Nanovehicles to Deliver Carbohydrate-Based Therapeutics and Vaccines

Cell-derived, nanoscale extracellular vesicles (EVs) have emerged as promising tools in diagnostic, therapeutic, and vaccine applications. Their unique properties including the capability to encapsulate diverse molecular cargo as well as the versatility in surface functionalization make them ideal candidates for safe and effective vehicles to deliver a range of biomolecules including gene editing cassettes, therapeutic proteins, glycans, and glycoconjugate vaccines. In this review, we discuss recent advances in the development of EVs derived from mammalian and bacterial cells for use in a delivery of carbohydrate-based protein therapeutics and vaccines. We highlight key innovations in EVs' molecular design, characterization, and deployment for treating diseases including Alzheimer's disease, infectious diseases, and cancers. We discuss challenges for their clinical translation and provide perspectives for future development of EVs within biopharmaceutical research and the clinical translation landscape.

Mitochondrial phosphatase PPTC7 promotes EGFR recycling by facilitating VPS4A endosomal localization

PPTC7 is a mitochondrial phosphatase that is essential for mitochondrial biogenesis, metabolism, protein content maintenance and transport. Although the mitochondrial roles of PPTC7 are well characterized, its roles outside the mitochondria are unclear. Here we identified a non-mitochondrial role for PPTC7 in regulating epidermal growth factor receptor (EGFR) trafficking. PPTC7 interacts with and dephosphorylates VPS4A, a crucial ESCRT and multivesicular body-associated protein. We found that PPTC7-mediated dephosphorylation of VPS4A at serine 335 is required for VPS4A stability and its early endosomal localization. Either loss of PPTC7 or presence of constitutively phosphorylated VPS4A led to defective recycling of EGFR, thus leading to EGFR re-routing to lysosomes for degradation. Further, we demonstrate that PPTC7-VPS4A-dependent EGFR recycling promotes the AKT signaling pathway, thus enhancing cell proliferation and migration. Overall, our studies unveil an important mechanism where the PPTC7-VPS4A complex orchestrates an endosomal switch to promote EGFR recycling.

Structural plasticity of bacterial ESCRT-III protein PspA in higher-order assemblies

Eukaryotic members of the endosome sorting complex required for transport-III (ESCRT-III) family have been shown to form diverse higher-order assemblies. The bacterial phage shock protein A (PspA) has been identified as a member of the ESCRT-III superfamily, and PspA homo-oligomerizes to form rod-shaped assemblies. As observed for eukaryotic ESCRT-III, PspA forms tubular assemblies of varying diameters. Using electron cryo-electron microscopy, we determined 61 Synechocystis PspA structures and observed in molecular detail how the structural plasticity of PspA rods is mediated by conformational changes at three hinge regions in the monomer and by the fixed and changing molecular contacts between protomers. Moreover, we reduced and increased the structural plasticity of PspA rods by removing the loop connecting helices α3/α4 and the addition of nucleotides, respectively. Based on our analysis of PspA-mediated membrane remodeling, we suggest that the observed mode of structural plasticity is a prerequisite for the biological function of ESCRT-III members.

Advances of M1 macrophages-derived extracellular vesicles in tumor therapy

Extracellular vesicles derived from classically activated M1 macrophages (M1 EVs) have shown great potential in both tumor treatment and drug delivery. M1 EVs inherit specific biological messengers from their parent cells and possess the capability to activate immune cells residing in close or distant tumor tissues for antitumor therapy. Moreover, M1 EVs are commonly used as an attractive drug delivery system due to their tumor-targeting ability, biocompatibility, and non-toxic. They can effectively encapsulate various therapeutic cargoes through specific methods such as electroporation, co-incubation, sonication, extrusion, transfection, or click chemistry reaction. In this review, we provide a comprehensive summary of the advancements in M1 EVs for tumor therapy, discussing their application prospects and existing problems.

PTPN23-dependent ESCRT machinery functions as a cell death checkpoint

Cell death plasticity is crucial for modulating tissue homeostasis and immune responses, but our understanding of the molecular components that regulate cell death pathways to determine cell fate remains limited. Here, a CRISPR screen of acute myeloid leukemia cells identifies protein tyrosine phosphatase non-receptor type 23 (PTPN23) as essential for survival. Loss of PTPN23 activates nuclear factor-kappa B, apoptotic, necroptotic, and pyroptotic pathways by causing the accumulation of death receptors and toll-like receptors (TLRs) in endosomes. These effects are recapitulated by depletion of PTPN23 co-dependent genes in the endosomal sorting complex required for transport (ESCRT) pathway. Through proximity-dependent biotin labeling, we show that NAK-associated protein 1 interacts with PTPN23 to facilitate endosomal sorting of tumor necrosis factor receptor 1 (TNFR1), sensitizing cells to TNF-α-induced cytotoxicity. Our findings reveal PTPN23-dependent ESCRT machinery as a cell death checkpoint that regulates the spatiotemporal distribution of death receptors and TLRs to restrain multiple cell death pathways.

Preserving Genome Integrity: Unveiling the Roles of ESCRT Machinery

The endosomal sorting complex required for transport (ESCRT) machinery is composed of an articulated architecture of proteins that assemble at multiple cellular sites. The ESCRT machinery is involved in pathways that are pivotal for the physiology of the cell, including vesicle transport, cell division, and membrane repair. The subunits of the ESCRT I complex are mainly responsible for anchoring the machinery to the action site. The ESCRT II subunits function to bridge and recruit the ESCRT III subunits. The latter are responsible for finalizing operations that, independently of the action site, involve the repair and fusion of membrane edges. In this review, we report on the data related to the activity of the ESCRT machinery at two sites: the nuclear membrane and the midbody and the bridge linking cells in the final stages of cytokinesis. In these contexts, the machinery plays a significant role for the protection of genome integrity by contributing to the control of the abscission checkpoint and to nuclear envelope reorganization and correlated resilience. Consistently, several studies show how the dysfunction of the ESCRT machinery causes genome damage and is a codriver of pathologies, such as laminopathies and cancer.

ESCRT-III: a versatile membrane remodeling machinery and its implications in cellular processes and diseases

The endosomal sorting complexes required for transport (ESCRT) machinery is an evolutionarily conserved cytosolic protein complex that plays a crucial role in membrane remodeling and scission events across eukaryotes. Initially discovered for its function in multivesicular body (MVB) formation, the ESCRT complex has since been implicated in a wide range of membrane-associated processes, including endocytosis, exocytosis, cytokinesis, and autophagy. Recent advances have elucidated the ESCRT assembly pathway and highlighted the distinct functions of the various ESCRT complexes and their associated partners. Among the ESCRT complexes, ESCRT-III stands out as a critical player in membrane remodeling, with its subunits assembled into higher-order multimers capable of bending and severing membranes. This review focuses on the ESCRT-III complex, exploring its diverse functions in cellular processes beyond MVB biogenesis. We delve into the molecular mechanisms underlying ESCRT-III-mediated membrane remodeling and highlight its emerging roles in processes such as viral budding, autophagosome closure, and cytokinetic abscission. We also discuss the implications of ESCRT-III dysregulation in neurodegenerative diseases. The versatile membrane remodeling capabilities of ESCRT-III across diverse cellular processes underscore its importance in maintaining proper cellular function. Furthermore, we highlight the promising potential of ESCRT-III as a therapeutic target for neurodegenerative diseases, offering insights into the treatments of the diseases and the technical applications in related research fields.

Mesenchymal Stem Cell-Derived Exosomes as Drug Delivery Vehicles in Disease Therapy

Exosomes are small vesicles containing proteins, nucleic acids, and biological lipids, which are responsible for intercellular communication. Studies have shown that exosomes can be utilized as effective drug delivery vehicles to accurately deliver therapeutic substances to target tissues, enhancing therapeutic effects and reducing side effects. Mesenchymal stem cells (MSCs) are a class of stem cells widely used for tissue engineering, regenerative medicine, and immunotherapy. Exosomes derived from MSCs have special immunomodulatory functions, low immunogenicity, the ability to penetrate tumor tissues, and high yield, which are expected to be engineered into efficient drug delivery systems. Despite the promising promise of MSC-derived exosomes, exploring their optimal preparation methods, drug-loading modalities, and therapeutic potential remains challenging. Therefore, this article reviews the related characteristics, preparation methods, application, and potential risks of MSC-derived exosomes as drug delivery systems in order to find potential therapeutic breakthroughs.

The role of exosomal molecular cargo in exosome biogenesis and disease diagnosis

Exosomes represent a type of extracellular vesicles derived from the endosomal pathway that transport diverse molecular cargoes such as proteins, lipids, and nucleic acids. These cargoes have emerged as crucial elements impacting disease diagnosis, treatment, and prognosis, and are integral to the process of exosome formation. This review delves into the essential molecular cargoes implicated in the phases of exosome production and release. Emphasis is placed on their significance as cancer biomarkers and potential therapeutic targets, accompanied by an exploration of the obstacles and feasible applications linked to these developments.

Alternative mechanisms of Notch activation by partitioning into distinct endosomal domains

Different membrane microdomain compositions provide unique environments that can regulate signaling receptor function. We identify microdomains on the endosome membrane of Drosophila endosomes, enriched in lipid-raft or clathrin/ESCRT-0, which are associated with Notch activation by distinct, ligand-independent mechanisms. Transfer of Notch between microdomains is regulated by Deltex and Suppressor of deltex ubiquitin ligases and is limited by a gate-keeper role for ESCRT complexes. Ubiquitination of Notch by Deltex recruits it to the clathrin/ESCRT-0 microdomain and enhances Notch activation by an ADAM10-independent/TRPML-dependent mechanism. This requirement for Deltex is bypassed by the downregulation of ESCRT-III. In contrast, while ESCRT-I depletion also activates Notch, it does so by an ADAM10-dependent/TRPML-independent mechanism and Notch is retained in the lipid raft-like microdomain. In the absence of such endosomal perturbation, different activating Notch mutations also localize to different microdomains and are activated by different mechanisms. Our findings demonstrate the interplay between Notch regulators, endosomal trafficking components, and Notch genetics, which defines membrane locations and activation mechanisms.

p-AKT/VPS4B regulates the small extracellular vesicle size in venous malformation endothelial cells

OBJECTIVE

Small extracellular vesicle (sEV)-mediated intercellular communication is increasingly the key for the understanding of venous malformations (VMs). This study aims to clarify the detailed changes of sEVs in VMs.

SUBJECTS AND METHODS

Fifteen VM patients without treatment history and twelve healthy donors were enrolled in the study. sEVs were isolated from both fresh lesions and cell supernatant, and were examined by western blotting, nanoparticle tracking analysis and transmission electron microscopy. Western blot analysis, immunohistochemistry and immunofluorescence were adopted to screening candidate regulator of sEV size. Specific inhibitors and siRNA were employed to validate the role of dysregulated p-AKT/vacuolar protein sorting-associated protein 4B (VPS4B) signaling on the size of sEVs in endothelial cells.

RESULTS

The size of sEVs derived from both VM lesion tissues and cell model was significantly increased. VPS4B, whose expression level was mostly significantly downregulated in VM endothelial cells, was responsible for the size change of sEVs. Targeting abnormal AKT activation corrected the size change of sEVs by recovering the expression level of VPS4B.

CONCLUSION

Downregulated VPS4B in endothelial cells, resulted from abnormally activated AKT signaling, contributed to the increased size of sEVs in VMs.

Extracellular Vesicles in Malaria: Shedding Light on Pathogenic Depths

Malaria, a life-threatening infectious disease caused by Plasmodium falciparum, remains a significant global health challenge, particularly in tropical and subtropical regions. The epidemiological data for 2021 revealed a staggering toll, with 247 million reported cases and 619,000 fatalities attributed to the disease. This formidable global health challenge continues to perplex researchers seeking a comprehensive understanding of its pathogenesis. Recent investigations have unveiled the pivotal role of extracellular vesicles (EVs) in this intricate landscape. These tiny, membrane-bound vesicles, secreted by diverse cells, emerge as pivotal communicators in malaria's pathogenic orchestra. This Review delves into the multifaceted roles of EVs in malaria pathogenesis, elucidating their impact on disease progression and immune modulation. Insights into EV involvement offer potential therapeutic and diagnostic strategies. Integrating this information identifies targets to mitigate malaria's global impact. Moreover, this Review explores the potential of EVs as diagnostic biomarkers and therapeutic targets in malaria. By deciphering the intricate dialogue facilitated by these vesicles, new avenues for intervention and novel strategies for disease management may emerge.

IST1 regulates select recycling pathways

ESCRTs (Endosomal Sorting Complex Required for Transports) are a modular set of protein complexes with membrane remodeling activities that include the formation and release of intraluminal vesicles (ILVs) to generate multivesicular endosomes. While most of the 12 ESCRT-III proteins are known to play roles in ILV formation, IST1 has been associated with a wider range of endosomal remodeling events. Here, we extend previous studies of IST1 function in endosomal trafficking and confirm that IST1, along with its binding partner CHMP1B, contributes to scission of early endosomal carriers. Functionally, depleting IST1 impaired delivery of transferrin receptor from early/sorting endosomes to the endocytic recycling compartment and instead increased its rapid recycling to the plasma membrane via peripheral endosomes enriched in the clathrin adaptor AP-1. IST1 is also important for export of mannose 6-phosphate receptor from early/sorting endosomes. Examination of IST1 binding partners on endosomes revealed that IST1 interacts with the MIT domain-containing sorting nexin SNX15, a protein previously reported to regulate endosomal recycling. Our kinetic and spatial analyses establish that SNX15 and IST1 occupy a clathrin-containing subdomain on the endosomal perimeter distinct from those previously implicated in cargo retrieval or degradation. Using live-cell microscopy, we see that SNX15 and CHMP1B alternately recruit IST1 to this subdomain or the base of endosomal tubules. These findings indicate that IST1 contributes to a subset of recycling pathways from the early/sorting endosome.

Insights into the function of ESCRT complex and LBPA in ASFV infection

The African swine fever virus (ASFV) is strongly dependent on an intact endocytic pathway and a certain cellular membrane remodeling for infection, possibly regulated by the endosomal sorting complexes required for transport (ESCRT). The ESCRT machinery is mainly involved in the coordination of membrane dynamics; hence, several viruses exploit this complex and its accessory proteins VPS4 and ALIX for their own benefit. In this work, we found that shRNA-mediated knockdown of VPS4A decreased ASFV replication and viral titers, and this silencing resulted in an enhanced expression of ESCRT-0 component HRS. ASFV infection slightly increased HRS expression but not under VPS4A depletion conditions. Interestingly, VPS4A silencing did not have an impact on ALIX expression, which was significantly overexpressed upon ASFV infection. Further analysis revealed that ALIX silencing impaired ASFV infection at late stages of the viral cycle, including replication and viral production. In addition to ESCRT, the accessory protein ALIX is involved in endosomal membrane dynamics in a lysobisphosphatydic acid (LBPA) and Ca2+-dependent manner, which is relevant for intraluminal vesicle (ILV) biogenesis and endosomal homeostasis. Moreover, LBPA interacts with NPC2 and/or ALIX to regulate cellular cholesterol traffic, and would affect ASFV infection. Thus, we show that LBPA blocking impacted ASFV infection at both early and late infection, suggesting a function for this unconventional phospholipid in the ASFV viral cycle. Here, we found for the first time that silencing of VPS4A and ALIX affects the infection later on, and blocking LBPA function reduces ASFV infectivity at early and later stages of the viral cycle, while ALIX was overexpressed upon infection. These data suggested the relevance of ESCRT-related proteins in ASFV infection.

Vps60 initiates alternative ESCRT-III filaments

Endosomal sorting complex required for transport-III (ESCRT-III) participates in essential cellular functions, from cell division to endosome maturation. The remarkable increase of its subunit diversity through evolution may have enabled the acquisition of novel functions. Here, we characterize a novel ESCRT-III copolymer initiated by Vps60. Membrane-bound Vps60 polymers recruit Vps2, Vps24, Did2, and Ist1, as previously shown for Snf7. Snf7- and Vps60-based filaments can coexist on membranes without interacting as their polymerization and recruitment of downstream subunits remain spatially and biochemically separated. In fibroblasts, Vps60/CHMP5 and Snf7/CHMP4 are both recruited during endosomal functions and cytokinesis, but their localization is segregated and their recruitment dynamics are different. Contrary to Snf7/CHMP4, Vps60/CHMP5 is not recruited during nuclear envelope reformation. Taken together, our results show that Vps60 and Snf7 form functionally distinct ESCRT-III polymers, supporting the notion that diversification of ESCRT-III subunits through evolution is linked to the acquisition of new cellular functions.

IST1 regulates select endosomal recycling pathways

ESCRTs (Endosomal Sorting Complex Required for Transport) are a modular set of protein complexes with membrane remodeling activities that include the formation and release of intralumenal vesicles (ILVs) to generate multivesicular endosomes. While most of the 12 ESCRT-III proteins are known to play roles in ILV formation, IST1 has been associated with a wider range of endosomal remodeling events. Here, we extend previous studies of IST1 function in endosomal trafficking and confirm that IST1, along with its binding partner CHMP1B, contributes to scission of early endosomal carriers. Depleting IST1 impaired delivery of transferrin receptor from early/sorting endosomes to the endocytic recycling compartment and instead increased its rapid recycling to the plasma membrane via peripheral endosomes enriched in the clathrin adaptor AP-1. IST1 is also important for export of mannose 6-phosphate receptor from early/sorting endosomes. Examination of IST1 binding partners on endosomes revealed that IST1 interacts with the MIT domain-containing sorting nexin SNX15, a protein previously reported to regulate endosomal recycling. Our kinetic and spatial analyses establish that SNX15 and IST1 occupy a clathrin-containing subdomain on the endosomal perimeter distinct from those previously implicated in cargo retrieval or degradation. Using live-cell microscopy we see that SNX15 and CHMP1B alternately recruit IST1 to this subdomain or the base of endosomal tubules. These findings indicate that IST1 contributes to a subset of recycling pathways from the early/sorting endosome.

Structure and dynamics of ESCRT-III membrane remodeling proteins by high-speed atomic force microscopy

Endosomal Sorting Complex Required for Transport (ESCRT) proteins assemble on the cytoplasmic leaflet of membranes and remodel them. ESCRT is involved in biological processes where membranes are bent away from the cytosol, constricted, and finally severed, such as in multi-vesicular body formation (in the endosomal pathway for protein sorting) or abscission during cell division. The ESCRT system is hijacked by enveloped viruses to allow buds of nascent virions to be constricted, severed and released. ESCRT-III proteins, the most downstream components of the ESCRT system, are monomeric and cytosolic in their autoinhibited conformation. They share a common architecture, a four-helix bundle with a fifth helix that interacts with this bundle to prevent polymerizing. Upon binding to negatively charged membranes, the ESCRT-III components adopt an activated state that allows them to polymerize into filaments and spirals, and to interact with the AAA-ATPase Vps4 for polymer remodeling. ESCRT-III has been studied with electron microscopy (EM) and fluorescence microscopy (FM); these methods provided invaluable information about ESCRT assembly structures or their dynamics, respectively, but neither approach provides detailed insights into both aspects simultaneously. High-speed atomic force microscopy (HS-AFM) has overcome this shortcoming, providing movies at high spatio-temporal resolution of biomolecular processes, significantly increasing our understanding of ESCRT-III structure and dynamics. Here, we review the contributions of HS-AFM in the analysis of ESCRT-III, focusing on recent developments of non-planar and deformable HS-AFM supports. We divide the HS-AFM observations into four sequential steps in the ESCRT-III lifecycle: 1) polymerization, 2) morphology, 3) dynamics, and 4) depolymerization.

The Machinery of Exosomes: Biogenesis, Release, and Uptake

Exosomes are a subtype of membrane-contained vesicles 40-200 nm in diameter that are secreted by cells into their surroundings. By transporting proteins, lipids, mRNA, miRNA, lncRNA, and DNA, exosomes are able to perform such vital functions as maintaining cellular homeostasis, removing cellular debris, and facilitating intercellular and interorgan communication. Exosomes travel in all body fluids and deliver their molecular messages in autocrine, paracrine as well as endocrine manners. In recent years, there has been an increased interest in studying exosomes as diagnostic markers and therapeutic targets, since in many disease conditions this machinery becomes dysregulated or hijacked by pathological processes. Additionally, delivery of exosomes and exosomal miRNA has already been shown to improve systemic metabolism and inhibit progression of cancer development in mice. However, the subcellular machinery of exosomes, including their biogenesis, release and uptake, remains largely unknown. This review will bring molecular details of these processes up to date with the goal of expanding the knowledge basis for designing impactful exosome experiments in the future.

Upregulation of the ESCRT pathway and multivesicular bodies accelerates degradation of proteins associated with neurodegeneration

Many neurodegenerative diseases, including Huntington's disease (HD) and Alzheimer's disease (AD), occur due to an accumulation of aggregation-prone proteins, which results in neuronal death. Studies in animal and cell models show that reducing the levels of these proteins mitigates disease phenotypes. We previously reported a small molecule, NCT-504, which reduces cellular levels of mutant huntingtin (mHTT) in patient fibroblasts as well as mouse striatal and cortical neurons from an Hdh^Q111 mutant mouse. Here, we show that NCT-504 has a broader potential, and in addition reduces levels of Tau, a protein associated with Alzheimer's disease, as well as other tauopathies. We find that in untreated cells, Tau and mHTT are degraded via autophagy. Notably, treatment with NCT-504 diverts these proteins to multivesicular bodies (MVB) and the ESCRT pathway. Specifically, NCT-504 causes a proliferation of endolysosomal organelles including MVB, and an enhanced association of mHTT and Tau with endosomes and MVB. Importantly, depletion of proteins that act late in the ESCRT pathway blocked NCT-504 dependent degradation of Tau. Moreover, NCT-504-mediated degradation of Tau occurred in cells where Atg7 is depleted, which indicates that this pathway is independent of canonical autophagy. Together, these studies reveal that upregulation of traffic through an ESCRT-dependent MVB pathway may provide a therapeutic approach for neurodegenerative diseases.

Structural basis of CHMP2A-CHMP3 ESCRT-III polymer assembly and membrane cleavage

The endosomal sorting complex required for transport (ESCRT) is a highly conserved protein machinery that drives a divers set of physiological and pathological membrane remodeling processes. However, the structural basis of ESCRT-III polymers stabilizing, constricting and cleaving negatively curved membranes is yet unknown. Here we present cryo-EM structures of membrane-coated CHMP2A-CHMP3 filaments from Homo sapiens of two different diameters at 3.3 and 3.6 Å resolution. The structures reveal helical filaments assembled by CHMP2A-CHMP3 heterodimers in the open ESCRT-III conformation, which generates a partially positive charged membrane interaction surface, positions short N-terminal motifs for membrane interaction and the C-terminal VPS4 target sequence toward the tube interior. Inter-filament interactions are electrostatic, which may facilitate filament sliding upon VPS4-mediated polymer remodeling. Fluorescence microscopy as well as high-speed atomic force microscopy imaging corroborate that VPS4 can constrict and cleave CHMP2A-CHMP3 membrane tubes. We therefore conclude that CHMP2A-CHMP3-VPS4 act as a minimal membrane fission machinery.

The Membrane Activity of the Amphibian Temporin B Peptide Analog TB_KKG6K Sheds Light on the Mechanism That Kills Candida albicans

Temporin B (TB) is a 13-amino-acid-long, cationic peptide secreted by the granular glands of the European frog Rana temporaria. We recently showed that the modified TB peptide analog TB_KKG6K rapidly killed planktonic and sessile Candida albicans at low micromolar concentrations and was neither hemolytic nor cytotoxic to mammalian cells in vitro. The present study aimed to shed light into its mechanism of action, with a focus on its fungal cell membrane activity. We utilized different fluorescent dyes to prove that it rapidly induces membrane depolarization and permeabilization. Studies on model membrane systems revealed that the TB analog undergoes hydrophobic and electrostatic membrane interactions, showing a preference for anionic lipids, and identified phosphatidylinositol and cardiolipin as possible peptide targets. Fluorescence microscopy using fluorescein isothiocyanate-labeled TB_KKG6K in the presence of the lipophilic dye FM4-64 indicated that the peptide compromises membrane integrity and rapidly enters C. albicans cells in an energy-independent manner. Peptide-treated cells analyzed by cryo-based electron microscopy exhibited no signs of cell lysis; however, subcellular structures had disintegrated, suggesting that intracellular activity may form part of the killing mechanism of the peptide. Taken together, this study proved that TB_KKG6K compromises C. albicans membrane function, which explains the previously observed rapid, fungicidal mode of action and supports its great potential as a future anti-Candida therapeutic. IMPORTANCE Fungal infections with the opportunistic human pathogen C. albicans are associated with high mortality rates in immunocompromised patients. This is partly due to the yeast's ability to rapidly develop resistance toward currently available antifungals. Small, cationic, membrane-active peptides are promising compounds to fight against resistance development, as many of them effectuate rapid fungal cell death. This fast killing is believed to hamper the development of resistance, as the fungi do not have sufficient time to adapt to the antifungal compound. We previously reported that the synthetic variant of the amphibian TB peptide, TB_KKG6K, rapidly kills C. albicans. In the current study, the mechanism of action of the TB analog was investigated. We show that this TB analog is membrane-active and impairs cell membrane function, highlighting its potential to be developed as an attractive alternative anti-C. albicans therapeutic that may hinder the development of resistance.

The roles of small extracellular vesicles as prognostic biomarkers and treatment approaches in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a particularly aggressive and invasive breast cancer subtype and is associated with poor clinical outcomes. Treatment approaches for TNBC remain limited partly due to the lack of expression of well-known molecular targets. Small extracellular vesicles (sEVs) carrying a variety of bioactive contents play an important role in intercellular communications. The biomolecules including nucleic acids, proteins, and metabolites can be transferred locally or systematically to recipient cells and regulate their biological states and are involved in physiological and pathological processes. Recently, despite the extensive attraction to the physiological functions of sEVs, few studies focus on the roles of sEVs in TNBC. In this review, we will summarize the involvement of sEVs in the tumor microenvironment of TNBC. Moreover, we will discuss the potential roles of sEVs as diagnostic markers and treatment therapy in this heterogeneous breast cancer subtype. We finally summarize the clinical application of sEVs in TNBC.

Comprehensive analysis of the human ESCRT-III-MIT domain interactome reveals new cofactors for cytokinetic abscission

The 12 related human ESCRT-III proteins form filaments that constrict membranes and mediate fission, including during cytokinetic abscission. The C-terminal tails of polymerized ESCRT-III subunits also bind proteins that contain Microtubule-Interacting and Trafficking (MIT) domains. MIT domains can interact with ESCRT-III tails in many different ways to create a complex binding code that is used to recruit essential cofactors to sites of ESCRT activity. Here, we have comprehensively and quantitatively mapped the interactions between all known ESCRT-III tails and 19 recombinant human MIT domains. We measured 228 pairwise interactions, quantified 60 positive interactions, and discovered 18 previously unreported interactions. We also report the crystal structure of the SPASTIN MIT domain in complex with the IST1 C-terminal tail. Three MIT enzymes were studied in detail and shown to: (1) localize to cytokinetic midbody membrane bridges through interactions with their specific ESCRT-III binding partners (SPASTIN-IST1, KATNA1-CHMP3, and CAPN7-IST1), (2) function in abscission (SPASTIN, KATNA1, and CAPN7), and (3) function in the 'NoCut' abscission checkpoint (SPASTIN and CAPN7). Our studies define the human MIT-ESCRT-III interactome, identify new factors and activities required for cytokinetic abscission and its regulation, and provide a platform for analyzing ESCRT-III and MIT cofactor interactions in all ESCRT-mediated processes.

Endocytic membrane repair by ESCRT-III controls antigen export to the cytosol during antigen cross-presentation

Despite its crucial role in initiation of cytotoxic immune responses, the molecular pathways underlying antigen cross-presentation remain incompletely understood. The mechanism of antigen exit from endocytic compartments into the cytosol is a long-standing matter of controversy, confronting two main models: transfer through specific channels/transporters or rupture of endocytic membranes and leakage of luminal content. By monitoring the occurrence of intracellular damage in conventional dendritic cells (cDCs), we show that cross-presenting cDC1s display more frequent endomembrane injuries and increased recruitment of endosomal sorting complex required for transport (ESCRT)-III, the main repair system for intracellular membranes, relative to cDC2s. Silencing of CHMP2a or CHMP4b, two effector subunits of ESCRT-III, enhances cytosolic antigen export and cross-presentation. This phenotype is partially reversed by chemical inhibition of RIPK3, suggesting that endocytic damage is related to basal activation of the necroptosis pathway. Membrane repair therefore proves crucial in containing antigen export to the cytosol and cross-presentation in cDCs.

Human Milk Extracellular Vesicles: A Biological System with Clinical Implications

The consumption of human milk by a breastfeeding infant is associated with positive health outcomes, including lower risk of diarrheal disease, respiratory disease, otitis media, and in later life, less risk of chronic disease. These benefits may be mediated by antibodies, glycoproteins, glycolipids, oligosaccharides, and leukocytes. More recently, human milk extracellular vesicles (hMEVs) have been identified. HMEVs contain functional cargos, i.e., miRNAs and proteins, that may transmit information from the mother to promote infant growth and development. Maternal health conditions can influence hMEV composition. This review summarizes hMEV biogenesis and functional contents, reviews the functional evidence of hMEVs in the maternal–infant health relationship, and discusses challenges and opportunities in hMEV research.

Using Drosophila melanogaster to Analyse the Human Paralogs of the ESCRT-III Core Component Shrub/CHMP4/Snf7 and Its Interactions with Members of the LGD/CC2D1 Family

The evolutionary conserved ESCRT-III complex is a device for membrane remodelling in various cellular processes, such as the formation of intraluminal vesicles (ILVs), cytokinesis, and membrane repair. The common theme of all these processes is the abscission of membrane away from the cytosol. At its heart in Drosophila is Shrub, CHMP4 in humans, which dynamically polymerises into filaments through electrostatic interactions among the protomers. For the full activity, Shrub/CHMP4 requires physical interaction with members of the Lgd protein family. This interaction is mediated by the odd-numbered DM14 domains of Lgd, which bind to the negative interaction surface of Shrub. While only one Lgd and one Shrub exist in the genome of Drosophila, mammals have two Lgd orthologs, LGD1/CC2D1B and LGD2/CC2D1A, as well as three CHMP4s in their genomes, CHMP4A, CHMP4B, and CHMP4C. The rationale for the diversification of the ESCRT components is not understood. We here use Drosophila as a model system to analyse the activity of the human orthologs of Shrub and Lgd at an organismal level. This enabled us to use the plethora of available techniques available for Drosophila. We present evidence that CHMP4B is the true ortholog of Shrub, while CHMP4A and CHMP4C have diverging activities. Nevertheless, CHMP4A and CHMP4C can enhance the activity of CHMP4B, raising the possibility that they can form heteropolymers in vivo. Our structure-function analysis of the LGD1 and LGD2 indicates that the C2 domain of the LGD proteins has a specific function beyond protein stability and subcellular localisation. Moreover, our data specify that CHMP4B interacts more efficiently with LGD1 than with LGD2.

The ESCRT Machinery: Remodeling, Repairing, and Sealing Membranes

The ESCRT machinery is an evolutionarily conserved membrane remodeling complex that is used by the cell to perform reverse membrane scission in essential processes like protein degradation, cell division, and release of enveloped retroviruses. ESCRT-III, together with the AAA ATPase VPS4, harbors the main remodeling and scission function of the ESCRT machinery, whereas early-acting ESCRTs mainly contribute to protein sorting and ESCRT-III recruitment through association with upstream targeting factors. Here, we review recent advances in our understanding of the molecular mechanisms that underlie membrane constriction and scission by ESCRT-III and describe the involvement of this machinery in the sealing and repairing of damaged cellular membranes, a key function to preserve cellular viability and organellar function.

Role of SNAREs in Unconventional Secretion-Focus on the VAMP7-Dependent Secretion

Intracellular membrane protein trafficking is crucial for both normal cellular physiology and cell-cell communication. The conventional secretory route follows transport from the Endoplasmic reticulum (ER) to the plasma membrane via the Golgi apparatus. Alternative modes of secretion which can bypass the need for passage through the Golgi apparatus have been collectively termed as Unconventional protein secretion (UPS). UPS can comprise of cargo without a signal peptide or proteins which escape the Golgi in spite of entering the ER. UPS has been classified further depending on the mode of transport. Type I and Type II unconventional secretion are non-vesicular and non-SNARE protein dependent whereas Type III and Type IV dependent on vesicles and on SNARE proteins. In this review, we focus on the Type III UPS which involves the import of cytoplasmic proteins in membrane carriers of autophagosomal/endosomal origin and release in the extracellular space following SNARE-dependent intracellular membrane fusion. We discuss the role of vesicular SNAREs with a strong focus on VAMP7, a vesicular SNARE involved in exosome, lysosome and autophagy mediated secretion. We further extend our discussion to the role of unconventional secretion in health and disease with emphasis on cancer and neurodegeneration.

An Updated View of the Importance of Vesicular Trafficking and Transport and Their Role in Immune-Mediated Diseases: Potential Therapeutic Interventions

Cellular trafficking is the set of processes of distributing different macromolecules by the cell. This process is highly regulated in cells, involving a system of organelles (endomembranous system), among which are a great variety of vesicles that can be secreted from the cell, giving rise to different types of extracellular vesicles (EVs) that can be captured by other cells to modulate their function. The cells of the immune system are especially sensitive to this cellular traffic, producing and releasing different classes of EVs, especially in disease states. There is growing interest in this field due to the therapeutic and translational possibilities it offers. Different ways of taking advantage of the understanding of cell trafficking and EVs are being investigated, and their use as biomarkers or therapeutic targets is being investigated. The objective of this review is to collect the latest results and knowledge in this area with a specific focus on immune-mediated diseases. Although some promising results have been obtained, further knowledge is still needed, at both the basic and translational levels, to understand and modulate cellular traffic and EVs for better clinical management of these patients.

Correlation of vacuole morphology with stomatal lineage development by whole-cell electron tomography

Stomatal movement is essential for plants to optimize transpiration and therefore photosynthesis. Rapid changes in the stomatal aperture are accompanied by adjustment of vacuole volume and morphology in guard cells (GCs). In Arabidopsis (Arabidopsis thaliana) leaf epidermis, stomatal development undergoes a cell-fate transition including four stomatal lineage cells: meristemoid, guard mother cell, young GC, and GC. Little is known about the mechanism underlying vacuole dynamics and vacuole formation during stomatal development. Here, we utilized whole-cell electron tomography (ET) analysis to elucidate vacuole morphology, formation, and development in different stages of stomatal lineage cells at nanometer resolution. The whole-cell ET models demonstrated that large vacuoles were generated from small vacuole stepwise fusion/maturation along stomatal development stages. Further ET analyses verified the existence of swollen intraluminal vesicles inside distinct vacuoles at certain developmental stages of stomatal lineage cells, implying a role of multivesicular body fusion in stomatal vacuole formation. Collectively, our findings demonstrate a mechanism mediating vacuole formation in Arabidopsis stomatal development and may shed light on the role of vacuoles in stomatal movement.

Cellular ESCRT components are recruited to regulate the endocytic trafficking and RNA replication compartment assembly during classical swine fever virus infection

As the important molecular machinery for membrane protein sorting in eukaryotic cells, the endosomal sorting and transport complexes (ESCRT-0/I/II/III and VPS4) usually participate in various replication stages of enveloped viruses, such as endocytosis and budding. The main subunit of ESCRT-I, Tsg101, has been previously revealed to play a role in the entry and replication of classical swine fever virus (CSFV). However, the effect of the whole ESCRT machinery during CSFV infection has not yet been well defined. Here, we systematically determine the effects of subunits of ESCRT on entry, replication, and budding of CSFV by genetic analysis. We show that EAP20 (VPS25) (ESCRT-II), CHMP4B and CHMP7 (ESCRT-III) regulate CSFV entry and assist vesicles in transporting CSFV from Clathrin, early endosomes, late endosomes to lysosomes. Importantly, we first demonstrate that HRS (ESCRT-0), VPS28 (ESCRT-I), VPS25 (ESCRT-II) and adaptor protein ALIX play important roles in the formation of virus replication complexes (VRC) together with CHMP2B/4B/7 (ESCRT-III), and VPS4A. Further analyses reveal these subunits interact with CSFV nonstructural proteins (NS) and locate in the endoplasmic reticulum, but not Golgi, suggesting the role of ESCRT in regulating VRC assembly. In addition, we demonstrate that VPS4A is close to lipid droplets (LDs), indicating the importance of lipid metabolism in the formation of VRC and nucleic acid production. Altogether, we draw a new picture of cellular ESCRT machinery in CSFV entry and VRC formation, which could provide alternative strategies for preventing and controlling the diseases caused by CSFV or other Pestivirus.

ESCRT machinery can be responsible for virus budding and participate in regulating virus entry. However, little has been reported on its effects on VRC formation. Here, we uncover the novel roles of ESCRT-III and VPS4A in VRC assembly and update the additional subunits involved in the intracellular trafficking of CSFV. These data indicate that the ESCRT machinery promotes CSFV replication by forming VRC, which making it become nuclease-insensitive to avoid the recognition by the host antiviral surveillance system and the destruction of the viral RNA. Furthermore, we first demonstrate that the roles of ESCRT components in the formation of VRC in swine Pestivirus. Our findings highlight the growing evidence of diverse interactions between ESCRT subunits and viral factors of Flaviviridae family, and provide alternative strategies for preventing and controlling the diseases caused by CSFV or other Pestivirus.

Tsg101/ESCRT-I recruitment regulated by the dual binding modes of K63-linked diubiquitin

The ESCRT-I protein Tsg101 plays a critical role in viral budding and endocytic sorting. Although Tsg101 is known to recognize monoubiquitin (Ub₁), here we show that it can also bind several diubiquitins (K48-Ub₂, N-Ub₂, and K63-Ub₂), with a preference for K63-linked Ub₂. The NMR structure of the Tsg101:K63-Ub₂ complex showed that while the Ub₁-binding site accommodates the distal domain of Ub₂, the proximal domain alternatively binds two different sites, the vestigial active site and an N-terminal helix. Mutation of each site results in distinct phenotypes regarding the recruitment of Tsg101 partners. Mutation in the vestigial active site abrogates interaction between Tsg101 and the HIV-1 protein Gag but not Hrs, a cellular protein. Mutation at the N-terminal helix alters Gag but not Hrs-Tsg101 localization. Given the broad involvement of Tsg101 in diverse cellular functions, this discovery advances our understanding of how the ESCRT protein recognizes binding partners and sorts endocytic cargo.

Bro1 binds the Vps20 subunit of ESCRT-III and promotes ESCRT-III regulation by Doa4

The budding of intralumenal vesicles (ILVs) at endosomes requires membrane scission by the ESCRT-III complex. This step is negatively regulated in yeast by Doa4, the ubiquitin hydrolase that deubiquitinates transmembrane proteins sorted as cargoes into ILVs. Doa4 acts non-enzymatically to inhibit ESCRT-III membrane scission activity by directly binding the Snf7 subunit of ESCRT-III. This interaction inhibits the remodeling/disassembly of Snf7 polymers required for the ILV membrane scission reaction. Thus, Doa4 is thought to have a structural role that delays ILV budding while it also functions enzymatically to deubiquitinate ILV cargoes. In this study, we show that Doa4 binding to Snf7 in vivo is antagonized by another ESCRT-III subunit, Vps20. Doa4 is restricted from interacting with Snf7 in yeast expressing a mutant Vps20 allele that constitutively binds Doa4. This inhibitory effect of Vps20 is suppressed by overexpression of another ESCRT-III-associated protein, Bro1. We show that Bro1 binds directly to Vps20, suggesting that Bro1 has a central role in relieving the antagonistic relationship that Vps20 has toward Doa4.

Dihydroceramide desaturase promotes the formation of intraluminal vesicles and inhibits autophagy to increase exosome production

Exosomes are important for cell-cell communication. Deficiencies in the human dihydroceramide desaturase gene, DEGS1, increase the dihydroceramide-to-ceramide ratio and cause hypomyelinating leukodystrophy. However, the disease mechanism remains unknown. Here, we developed an in vivo assay with spatially controlled expression of exosome markers in Drosophila eye imaginal discs and showed that the level and activity of the DEGS1 ortholog, Ifc, correlated with exosome production. Knocking out ifc decreased the density of the exosome precursor intraluminal vesicles (ILVs) in the multivesicular endosomes (MVEs) and reduced the number of exosomes released. While ifc overexpression and autophagy inhibition both enhanced exosome production, combining the two had no additive effect. Moreover, DEGS1 activity was sufficient to drive ILV formation in vitro. Together, DEGS1/Ifc controls the dihydroceramide-to-ceramide ratio and enhances exosome secretion by promoting ILV formation and preventing the autophagic degradation of MVEs. These findings provide a potential cause for the neuropathy associated with DEGS1-deficient mutations.

Cell-Matrix Interactions Regulate Functional Extracellular Vesicle Secretion from Mesenchymal Stromal Cells

Extracellular vesicles (EVs) are cell-secreted particles with broad potential to treat tissue injuries by delivering cargo to program target cells. However, improving the yield of functional EVs on a per cell basis remains challenging due to an incomplete understanding of how microenvironmental cues regulate EV secretion at the nanoscale. We show that mesenchymal stromal cells (MSCs) seeded on engineered hydrogels that mimic the elasticity of soft tissues with a lower integrin ligand density secrete ∼10-fold more EVs per cell than MSCs seeded on a rigid plastic substrate, without compromising their therapeutic activity or cargo to resolve acute lung injury in mice. Mechanistically, intracellular CD63⁺ multivesicular bodies (MVBs) transport faster within MSCs on softer hydrogels, leading to an increased frequency of MVB fusion with the plasma membrane to secrete more EVs. Actin-related protein 2/3 complex but not myosin-II limits MVB transport and EV secretion from MSCs on hydrogels. The results provide a rational basis for biomaterial design to improve EV secretion while maintaining their functionality.

Archaeal extracellular vesicles are produced in an ESCRT-dependent manner and promote gene transfer and nutrient cycling in extreme environments

Membrane-bound extracellular vesicles (EVs), secreted by cells from all three domains of life, transport various molecules and act as agents of intercellular communication in diverse environments. Here we demonstrate that EVs produced by a hyperthermophilic and acidophilic archaeon Sulfolobus islandicus carry not only a diverse proteome, enriched in membrane proteins, but also chromosomal and plasmid DNA, and can transfer this DNA to recipient cells. Furthermore, we show that EVs can support the heterotrophic growth of Sulfolobus in minimal medium, implicating EVs in carbon and nitrogen fluxes in extreme environments. Finally, our results indicate that, similar to eukaryotes, production of EVs in S. islandicus depends on the archaeal ESCRT machinery. We find that all components of the ESCRT apparatus are encapsidated into EVs. Using synchronized S. islandicus cultures, we show that EV production is linked to cell division and appears to be triggered by increased expression of ESCRT proteins during this cell cycle phase. Using a CRISPR-based knockdown system, we show that archaeal ESCRT-III and AAA+ ATPase Vps4 are required for EV production, whereas archaea-specific component CdvA appears to be dispensable. In particular, the active EV production appears to coincide with the expression patterns of ESCRT-III-1 and ESCRT-III-2, rather than ESCRT-III, suggesting a prime role of these proteins in EV budding. Collectively, our results suggest that ESCRT-mediated EV biogenesis has deep evolutionary roots, likely predating the divergence of eukaryotes and archaea, and that EVs play an important role in horizontal gene transfer and nutrient cycling in extreme environments.

Held Up in Traffic-Defects in the Trafficking Machinery in Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth disease (CMT), also known as motor and sensory neuropathy, describes a clinically and genetically heterogenous group of disorders affecting the peripheral nervous system. CMT typically arises in early adulthood and is manifested by progressive loss of motor and sensory functions; however, the mechanisms leading to the pathogenesis are not fully understood. In this review, we discuss disrupted intracellular transport as a common denominator in the pathogenesis of different CMT subtypes. Intracellular transport via the endosomal system is essential for the delivery of lipids, proteins, and organelles bidirectionally to synapses and the soma. As neurons of the peripheral nervous system are amongst the longest neurons in the human body, they are particularly susceptible to damage of the intracellular transport system, leading to a loss in axonal integrity and neuronal death. Interestingly, defects in intracellular transport, both in neurons and Schwann cells, have been found to provoke disease. This review explains the mechanisms of trafficking and subsequently summarizes and discusses the latest findings on how defects in trafficking lead to CMT. A deeper understanding of intracellular trafficking defects in CMT will expand our understanding of CMT pathogenesis and will provide novel approaches for therapeutic treatments.

Importance of Viral Late Domains in Budding and Release of Enveloped RNA Viruses

Late assembly (L) domains are conserved sequences that are necessary for the late steps of viral replication, acting like cellular adaptors to engage the ESCRT membrane fission machinery that promote virion release. These short sequences, whose mutation or deletion produce the accumulation of immature virions at the plasma membrane, were firstly identified within retroviral Gag precursors, and in a further step, also in structural proteins of many other enveloped RNA viruses including arenaviruses, filoviruses, rhabdoviruses, reoviruses, and paramyxoviruses. Three classes of L domains have been identified thus far (PT/SAP, YPXnL/LXXLF, and PPxY), even if it has recently been suggested that other motifs could act as L domains. Here, we summarize the current state of knowledge of the different types of L domains and their cellular partners in the budding events of RNA viruses, with a particular focus on retroviruses.

ESCRT-III induces phase separation in model membranes prior to budding and causes invagination of the liquid-ordered phase

Membrane fission triggered by the endosomal sorting complex required for transport (ESCRT) is an important process observed in several pathogenic and non-pathogenic cellular events. From a synthetic-biology viewpoint, ESCRT proteins represent an interesting machinery for the construction of cell mimetic sub-compartments produced by fission. Since their discovery, the studies on ESCRT-III-mediated action, have mainly focused on protein dynamics, ignoring the role of lipid organization and membrane phase state. Recently, it has been suggested that membrane buds formed by the action of ESCRT-III are generated from transient microdomains in endosomal membranes. However, the interplay between membrane domain formation and ESCRT remodeling pathways has not been investigated. Here, giant unilamellar vesicles made of ternary lipid mixtures, either homogeneous in phase or exhibiting liquid-ordered/liquid-disordered phase coexistence, were employed as a model membrane system. These vesicles were incubated with purified recombinant ESCRT-III proteins from the parasite Entamoeba histolytica. In homogeneous membranes, we observe that EhVps32 can trigger domain formation while EhVps20 preferentially co-localizes in the liquid disordered phase. The addition of EhVps24 appears to induce the formation of intraluminal vesicles produced from the liquid-ordered phase. In phase separated membranes, the intraluminal vesicles are also generated from the liquid-ordered phase and presumably emerge from the phase boundary region. Our findings reinforce the hypothesis that ESCRT-mediated remodeling depends on the membrane phase state. Furthermore, the obtained results point to a potential synthetic biology approach for establishing eukaryotic mimics of artificial cells with microcompartments of specific membrane composition, which can also differ from that of the mother vesicle.

Current Knowledge of Endolysosomal and Autophagy Defects in Hereditary Spastic Paraplegia

Hereditary spastic paraplegia (HSP) refers to a group of neurological disorders involving the degeneration of motor neurons. Due to their clinical and genetic heterogeneity, finding common effective therapeutics is difficult. Therefore, a better understanding of the common pathological mechanisms is necessary. The role of several HSP genes/proteins is linked to the endolysosomal and autophagic pathways, suggesting a functional convergence. Furthermore, impairment of these pathways is particularly interesting since it has been linked to other neurodegenerative diseases, which would suggest that the nervous system is particularly sensitive to the disruption of the endolysosomal and autophagic systems. In this review, we will summarize the involvement of HSP proteins in the endolysosomal and autophagic pathways in order to clarify their functioning and decipher some of the pathological mechanisms leading to HSP.

Design principles of the ESCRT-III Vps24-Vps2 module

ESCRT-III polymerization is required for all endosomal sorting complex required for transport (ESCRT)-dependent events in the cell. However, the relative contributions of the eight ESCRT-III subunits differ between each process. The minimal features of ESCRT-III proteins necessary for function and the role for the multiple ESCRT-III subunits remain unclear. To identify essential features of ESCRT-III subunits, we previously studied the polymerization mechanisms of two ESCRT-III subunits Snf7 and Vps24, identifying the association of the helix-4 region of Snf7 with the helix-1 region of Vps24 (Banjade et al., 2019a). Here, we find that mutations in the helix-1 region of another ESCRT-III subunit Vps2 can functionally replace Vps24 in Saccharomyces cerevisiae. Engineering and genetic selections revealed the required features of both subunits. Our data allow us to propose three minimal features required for ESCRT-III function – spiral formation, lateral association of the spirals through heteropolymerization, and binding to the AAA + ATPase Vps4 for dynamic remodeling.

Biogenesis, Membrane Trafficking, Functions, and Next Generation Nanotherapeutics Medicine of Extracellular Vesicles

Extracellular vesicles (EVs) are a heterogeneous group of membrane-limited vesicles and multi-signal messengers loaded with biomolecules. Exosomes and ectosomes are two different types of EVs generated by all cell types. Their formation depends on local microdomains assembled in endocytic membranes for exosomes and in the plasma membrane for ectosomes. Further, EV release is a fundamental process required for intercellular communication in both normal physiology and pathological conditions to transmit/exchange bioactive molecules to recipient cells and the extracellular environment. The unique structure and composition of EVs enable them to serve as natural nanocarriers, and their physicochemical properties and biological functions can be used to develop next-generation nano and precision medicine. Knowledge of the cellular processes that govern EVs biology and membrane trafficking is essential for their clinical applications. However, in this rapidly expanding field, much remains unknown regarding EV origin, biogenesis, cargo sorting, and secretion, as well as EV-based theranostic platform generation. Hence, we present a comprehensive overview of the recent advances in biogenesis, membrane trafficking, and functions of EVs, highlighting the impact of nanoparticles and oxidative stress on EVs biogenesis and release and finally emphasizing the role of EVs as nanotherapeutic agents.

Principles of membrane remodeling by dynamic ESCRT-III polymers

Endosomal protein complex required for transport-III (ESCRT-III) polymers are involved in many crucial cellular functions, from cell division to endosome-lysosome dynamics. As a eukaryotic membrane remodeling machinery, ESCRT-III is unique in its ability to catalyze fission of membrane necks from their luminal side and to participate in membrane remodeling processes of essentially all cellular organelles. Found in Archaea, it is also the most evolutionary ancient membrane remodeling machinery. The simple protein structure shared by all of its subunits assembles into a large variety of filament shapes, limiting our understanding of how these filaments achieve membrane remodeling. Here, we review recent findings that discovered unpredicted properties of ESCRT-III polymers, which enable us to define general principles of the mechanism by which ESCRT-III filaments remodel membranes.

Cdc42 GTPase regulates ESCRTs in nuclear envelope sealing and ER remodeling

Small GTPases of the Rho family are binary molecular switches that regulate a variety of processes including cell migration and oriented cell divisions. Known Cdc42 effectors include proteins involved in cytoskeletal remodeling and kinase-dependent transcription induction, but none are involved in the maintenance of nuclear envelope integrity or ER morphology. Maintenance of nuclear envelope integrity requires the EndoSomal Complexes Required for Transport (ESCRT) proteins, but how they are regulated in this process remains unknown. Here, we show by live-cell imaging a novel Cdc42 localization with ESCRT proteins at sites of nuclear envelope and ER fission and, by genetic analysis of cdc42 mutant yeast, uncover a unique Cdc42 function in regulation of ESCRT proteins at the nuclear envelope and sites of ER tubule fission. Our findings implicate Cdc42 in nuclear envelope sealing and ER remodeling, where it regulates ESCRT disassembly to maintain nuclear envelope integrity and proper ER architecture.

Extracellular Vesicles in Inflammatory Bowel Disease: Small Particles, Big Players

Extracellular vesicles are nanovesicles released by many cell types into the extracellular space. They are important mediators of intercellular communication, enabling the functional transfer of molecules from one cell to another. Moreover, their molecular composition reflects the physiological status of the producing cell and tissue. Consequently, these vesicles have been involved in many [patho]physiological processes such as immunomodulation and intestinal epithelial repair, both key processes involved in inflammatory bowel disease. Given that these vesicles are present in many body fluids, they also provide opportunities for diagnostic, prognostic, and therapeutic applications. In this review, we summarise functional roles of extracellular vesicles in health and disease, with a focus on immune regulation and intestinal barrier integrity, and review recent studies on extracellular vesicles and inflammatory bowel disease. We also elaborate on their clinical potential in inflammatory bowel disease.

Mechanobiology of Autophagy: The Unexplored Side of Cancer

Proper execution of cellular function, maintenance of cellular homeostasis and cell survival depend on functional integration of cellular processes and correct orchestration of cellular responses to stresses. Cancer transformation is a common negative consequence of mismanagement of coordinated response by the cell. In this scenario, by maintaining the balance among synthesis, degradation, and recycling of cytosolic components including proteins, lipids, and organelles the process of autophagy plays a central role. Several environmental stresses activate autophagy, among those hypoxia, DNA damage, inflammation, and metabolic challenges such as starvation. In addition to these chemical challenges, there is a requirement for cells to cope with mechanical stresses stemming from their microenvironment. Cells accomplish this task by activating an intrinsic mechanical response mediated by cytoskeleton active processes and through mechanosensitive protein complexes which interface the cells with their mechano-environment. Despite autophagy and cell mechanics being known to play crucial transforming roles during oncogenesis and malignant progression their interplay is largely overlooked. In this review, we highlight the role of physical forces in autophagy regulation and their potential implications in both physiological as well as pathological conditions. By taking a mechanical perspective, we wish to stimulate novel questions to further the investigation of the mechanical requirements of autophagy and appreciate the extent to which mechanical signals affect this process.