Methylation of ESCRT-III components regulates the timing of cytokinetic abscission

Abscission is the final stage of cytokinesis, which cleaves the intercellular bridge (ICB) connecting two daughter cells. Abscission requires tight control of the recruitment and polymerization of the Endosomal Protein Complex Required for Transport-III (ESCRT-III) components. We explore the role of post-translational modifications in regulating ESCRT dynamics. We discover that SMYD2 methylates the lysine 6 residue of human CHMP2B, a key ESCRT-III component, at the ICB, impacting the dynamic relocation of CHMP2B to sites of abscission. SMYD2 loss-of-function (genetically or pharmacologically) causes CHMP2B hypomethylation, delayed CHMP2B polymerization and delayed abscission. This is phenocopied by CHMP2B lysine 6 mutants that cannot be methylated. Conversely, SMYD2 gain-of-function causes CHMP2B hypermethylation and accelerated abscission, specifically in cells undergoing cytokinetic challenges, thereby bypassing the abscission checkpoint. Additional experiments highlight the importance of CHMP2B methylation beyond cytokinesis, namely during ESCRT-III-mediated HIV-1 budding. We propose that lysine methylation signaling fine-tunes the ESCRT-III machinery to regulate the timing of cytokinetic abscission and other ESCRT-III dependent functions.

Essential role of Alix in regulating cardiomyocyte exosome biogenesis under physiological and stress conditions

BACKGROUND

Exosomes released by cardiomyocytes are essential mediators of intercellular communications within the heart, and various exosomal proteins and miRNAs are associated with cardiovascular diseases. However, whether the endosomal sorting complex required for transport (ESCRT) and its key component Alix is required for exosome biogenesis within cardiomyocyte remains poorly understood.

METHODS

Super-resolution imaging was performed to investigate the subcellular location of Alix and multivesicular body (MVB) in primary cardiomyocytes. Cardiomyocyte-specific Alix-knockout mice were generated using AAV9/CRISPR/Cas9-mediated in vivo gene editing. A stable Alix-knockdown H9c2 cardiomyocyte line was constructed through lentiviral-mediated delivery of short hairpin RNA. In order to determine the role of Alix in controlling exosome biogenesis, exosomes from cardiomyocyte-specific Alix-knockout mice plasma and Alix-knockdown H9c2 culture medium were isolated and examined by western blot, NTA analysis and transmission electron microscopy. Biochemical and immunofluorescence analysis were performed to determine the role of ESCRT machinery in regulating MVB formation. Lastly, transverse aortic constriction (TAC)-induced cardiac pressure overload model was established to further explore the role of Alix-mediated exosome biogenesis under stress conditions.

RESULTS

A significant proportion of Alix localized to the MVB membrane within cardiomyocytes. Genetic deletion of Alix in murine heart resulted in a reduction of plasma exosome content without affecting cardiac structure or contractile function. Consistently, the downregulation of Alix in H9c2 cardiomyocyte line also suppressed the biogenesis of exosomes. We found the defective ESCRT machinery and suppressed MVB formation upon Alix depletion caused compromised exosome biogenesis. Remarkably, TAC-induced cardiac pressure overload led to increased Alix, MVB levels, and elevated plasma exosome content, which could be totally abolished by Alix deletion.

CONCLUSION

These results establish Alix as an essential and stress-sensitive regulator of cardiac exosome biogenesis and the findings may yield valuable therapeutic implications.

Lethal Giant Disc is a target of Cdk1 and regulates ESCRT-III localization during germline stem cell abscission

Abscission is the final step of cytokinesis that allows the physical separation of sister cells through the scission of the cellular membrane. This deformation is driven by ESCRT-III proteins, which can bind membranes and form dynamic helices. A crucial step in abscission is the recruitment of ESCRT-III proteins at the right time and place. Alix is one of the best characterized proteins that recruits ESCRT-III proteins from yeast to mammals. However, recent studies in vivo have revealed that pathways acting independently or redundantly with Alix are also required at abscission sites in different cellular contexts. Here, we show that Lgd acts redundantly with Alix to properly localize ESCRT-III to the abscission site in germline stem cells (GSCs) during Drosophila oogenesis. We further demonstrate that Lgd is phosphorylated at multiple sites by the CycB/Cdk1 kinase. We found that these phosphorylation events potentiate the activity of Shrub, a Drosophila ESCRT-III, during abscission of GSCs. Our study reveals that redundancy between Lgd and Alix, and coordination with the cell cycle kinase Cdk1, confers robust and timely abscission of Drosophila germline stem cells.

Sit4 Genetically Interacts with Vps27 to Regulate Mitochondrial Function and Lifespan in Saccharomyces cerevisiae

The Sit4 protein phosphatase plays a key role in orchestrating various cellular processes essential for maintaining cell viability during aging. We have previously shown that SIT4 deletion promotes vacuolar acidification, mitochondrial derepression, and oxidative stress resistance, increasing yeast chronological lifespan. In this study, we performed a proteomic analysis of isolated vacuoles and yeast genetic interaction analysis to unravel how Sit4 influences vacuolar and mitochondrial function. By employing high-resolution mass spectrometry, we show that sit4Δ vacuolar membranes were enriched in Vps27 and Hse1, two proteins that are part of the endosomal sorting complex required for transport-0. In addition, SIT4 exhibited a negative genetic interaction with VPS27, as sit4∆vps27∆ double mutants had a shortened lifespan compared to sit4∆ and vps27∆ single mutants. Our results also show that Vps27 did not increase sit4∆ lifespan by improving protein trafficking or vacuolar sorting pathways. However, Vps27 was critical for iron homeostasis and mitochondrial function in sit4∆ cells, as sit4∆vps27∆ double mutants exhibited high iron levels and impaired mitochondrial respiration. These findings show, for the first time, cross-talk between Sit4 and Vps27, providing new insights into the mechanisms governing chronological lifespan.

A role for Vps13-mediated lipid transfer at the ER-endosome contact site in ESCRT-mediated sorting

Endosomes are specialized organelles that function in the secretory and endocytic protein sorting pathways. Endocytosed cell surface receptors and transporters destined for lysosomal degradation are sorted into intraluminal vesicles (ILVs) at endosomes by endosomal sorting complexes required for transport (ESCRT) proteins. The endosomes (multivesicular bodies, MVBs) then fuse with the lysosome. During endosomal maturation, the number of ILVs increases, but the size of endosomes does not decrease despite the consumption of the limiting membrane during ILV formation. Vesicle-mediated trafficking is thought to provide lipids to support MVB biogenesis. However, we have uncovered an unexpected contribution of a large bridge-like lipid transfer protein, Vps13, in this process. Here, we reveal that Vps13-mediated lipid transfer at ER-endosome contact sites is required for the ESCRT pathway. We propose that Vps13 may play a critical role in supplying lipids to the endosome, ensuring continuous ESCRT-mediated sorting during MVB biogenesis.

The human AAA-ATPase VPS4A isoform and its co-factor VTA1 have a unique function in regulating mammalian cytokinesis abscission

Mutations in the human AAA-ATPase VPS4 isoform, VPS4A, cause severe neurodevelopmental defects and congenital dyserythropoietic anemia (CDA). VPS4 is a crucial component of the endosomal sorting complex required for transport (ESCRT) system, which drives membrane remodeling in numerous cellular processes, including receptor degradation, cell division, and neural pruning. Notably, while most organisms encode for a single VPS4 gene, human cells have 2 VPS4 paralogs, namely VPS4A and VPS4B, but the functional differences between these paralogs is mostly unknown. Here, we set out to investigate the role of the human VPS4 paralogs in cytokinetic abscission using a series of knockout cell lines. We found that VPS4A and VPS4B hold both overlapping and distinct roles in abscission. VPS4A depletion resulted in a more severe abscission delay than VPS4B and was found to be involved in earlier stages of abscission. Moreover, VPS4A and a monomeric-locked VPS4A mutant bound the abscission checkpoint proteins CHMP4C and ANCHR, while VPS4B did not, indicating a regulatory role for the VPS4A isoform in abscission. Depletion of VTA1, a co-factor of VPS4, disrupted VPS4A-ANCHR interactions and accelerated abscission, suggesting that VTA1 is also involved in the abscission regulation. Our findings reveal a dual role for VPS4A in abscission, one that is canonical and can be compensated by VPS4B, and another that is regulatory and may be delivered by its monomeric form. These observations provide a potential mechanistic explanation for the neurodevelopmental defects and other related disorders reported in VPS4A-mutated patients with a fully functional VPS4B paralog.

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.

Identification of membrane curvature sensing motifs essential for VPS37A phagophore recruitment and autophagosome closure

VPS37A, an ESCRT-I complex component, is required for recruiting a subset of ESCRT proteins to the phagophore for autophagosome closure. However, the mechanism by which VPS37A is targeted to the phagophore remains obscure. Here, we demonstrate that the VPS37A N-terminal domain exhibits selective interactions with highly curved membranes, mediated by two membrane-interacting motifs within the disordered regions surrounding its Ubiquitin E2 variant-like (UEVL) domain. Site-directed mutations of residues in these motifs disrupt ESCRT-I localization to the phagophore and result in defective phagophore closure and compromised autophagic flux in vivo, highlighting their essential role during autophagy. In conjunction with the UEVL domain, we postulate that these motifs guide a functional assembly of the ESCRT machinery at the highly curved tip of the phagophore for autophagosome closure. These results advance the notion that the distinctive membrane architecture of the cup-shaped phagophore spatially regulates autophagosome biogenesis.

Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy

The endosomal sorting complex required for transport (ESCRT) machinery is essential for membrane remodeling and autophagy and it comprises three multi-subunit complexes (ESCRT I-III). We report nine individuals from six families presenting with a spectrum of neurodevelopmental/neurodegenerative features caused by bi-allelic variants in SNF8 (GenBank: NM_007241.4), encoding the ESCRT-II subunit SNF8. The phenotypic spectrum included four individuals with severe developmental and epileptic encephalopathy, massive reduction of white matter, hypo-/aplasia of the corpus callosum, neurodevelopmental arrest, and early death. A second cohort shows a milder phenotype with intellectual disability, childhood-onset optic atrophy, or ataxia. All mildly affected individuals shared the same hypomorphic variant, c.304G>A (p.Val102Ile). In patient-derived fibroblasts, bi-allelic SNF8 variants cause loss of ESCRT-II subunits. Snf8 loss of function in zebrafish results in global developmental delay and altered embryo morphology, impaired optic nerve development, and reduced forebrain size. In vivo experiments corroborated the pathogenicity of the tested SNF8 variants and their variable impact on embryo development, validating the observed clinical heterogeneity. Taken together, we conclude that loss of ESCRT-II due to bi-allelic SNF8 variants is associated with a spectrum of neurodevelopmental/neurodegenerative phenotypes mediated likely via impairment of the autophagic flux.

USP8 prevents aberrant NF-κB and Nrf2 activation by counteracting ubiquitin signals from endosomes

K63-linked ubiquitin chains attached to plasma membrane proteins serve as tags for endocytosis and endosome-to-lysosome sorting. USP8 is an essential deubiquitinase for the maintenance of endosomal functions. Prolonged depletion of USP8 leads to cell death, but the major effects on cellular signaling pathways are poorly understood. Here, we show that USP8 depletion causes aberrant accumulation of K63-linked ubiquitin chains on endosomes and induces immune and stress responses. Upon USP8 depletion, two different decoders for K63-linked ubiquitin chains, TAB2/3 and p62, were recruited to endosomes and activated the TAK1-NF-κB and Keap1-Nrf2 pathways, respectively. Oxidative stress, an environmental stimulus that potentially suppresses USP8 activity, induced accumulation of K63-linked ubiquitin chains on endosomes, recruitment of TAB2, and expression of the inflammatory cytokine. The results demonstrate that USP8 is a gatekeeper of misdirected ubiquitin signals and inhibits immune and stress response pathways by removing K63-linked ubiquitin chains from endosomes.

The alleles bc-ud and bc-ur (previously bc-4 gene), representing coding mutations within Vps4 AAA+ ATPase ESCRT protein, interact with other genes to condition resistance to BCMV and BCMNV in common bean

Bean common mosaic virus (BCMV) and bean common mosaic necrosis virus (BCMNV) have a damaging impact on global common bean (Phaseolus vulgaris L.) cultivation, causing potential yield losses of over 80%. The primary strategy for controlling these viruses is through host plant resistance. This research aimed to identify and validate structural variations for the bc-ud gene as revealed by long-read sequencing, develop an efficient DNA marker to assist selection of bc-ud in snap and dry beans, and examine the interactions between the bc-ud allele and other BCMV resistance genes. A gene (Phvul.005G125100) model on chromosome Pv05, encoding a vacuolar protein-sorting 4 (Vps4) AAA+ ATPase endosomal sorting complexes required for transport (ESCRT) protein, was identified as the best candidate gene for bc-ud. An 84-bp repetitive insertion variant within the gene, exhibited 100% co-segregation with the bc-ud resistance allele across 264 common bean accessions. The 84-bp repetitive insertion was labeled with an indel marker IND_05_36225873 which was useful for tracking the bc-ud allele across diverse germplasm. A different single nucleotide polymorphism variant within the same candidate gene was associated with the bc-4 gene. Segregation in F2 populations confirmed bc-ud and bc-4 were alleles, so bc-4 was renamed bc-ur to fit gene nomenclature guidelines. The interactions of bc-ud and bc-ur with other resistance genes, such as bc-1 (receptor-like kinase on Pv03) and bc-2 (Vps4 AAA+ ATPase ESCRT protein on Pv11), validated gene combinations in the differential "host groups" effective against specific BCMV/BCMNV "pathogroups." These findings increase our understanding of the Bc-u locus, and enhance our ability to develop more resilient bean varieties through marker-assisted selection, reducing the impact of BCMV and BCMNV.

Plasma membrane damage limits replicative lifespan in yeast and induces premature senescence in human fibroblasts

Plasma membrane damage (PMD) occurs in all cell types due to environmental perturbation and cell-autonomous activities. However, cellular outcomes of PMD remain largely unknown except for recovery or death. In this study, using budding yeast and normal human fibroblasts, we found that cellular senescence-stable cell cycle arrest contributing to organismal aging-is the long-term outcome of PMD. Our genetic screening using budding yeast unexpectedly identified a close genetic association between PMD response and replicative lifespan regulations. Furthermore, PMD limits replicative lifespan in budding yeast; upregulation of membrane repair factors ESCRT-III (SNF7) and AAA-ATPase (VPS4) extends it. In normal human fibroblasts, PMD induces premature senescence via the Ca2+-p53 axis but not the major senescence pathway, DNA damage response pathway. Transient upregulation of ESCRT-III (CHMP4B) suppressed PMD-dependent senescence. Together with mRNA sequencing results, our study highlights an underappreciated but ubiquitous senescent cell subtype: PMD-dependent senescent cells.

Mechanism and cellular function of direct membrane binding by the ESCRT and ERES-associated Ca2+-sensor ALG-2

Apoptosis linked Gene-2 (ALG-2) is a multifunctional intracellular Ca2+ sensor and the archetypal member of the penta-EF hand protein family. ALG-2 functions in the repair of damage to both the plasma and lysosome membranes and in COPII-dependent budding at endoplasmic reticulum exit sites (ERES). In the presence of Ca2+, ALG-2 binds to ESCRT-I and ALIX in membrane repair and to SEC31A at ERES. ALG-2 also binds directly to acidic membranes in the presence of Ca2+ by a combination of electrostatic and hydrophobic interactions. By combining giant unilamellar vesicle-based experiments and molecular dynamics simulations, we show that charge-reversed mutants of ALG-2 at these locations disrupt membrane recruitment. ALG-2 membrane binding mutants have reduced or abrogated ERES localization in response to Thapsigargin-induced Ca2+ release but still localize to lysosomes following lysosomal Ca2+ release. In vitro reconstitution shows that the ALG-2 membrane-binding defect can be rescued by binding to ESCRT-I. These data thus reveal the nature of direct Ca2+-dependent membrane binding and its interplay with Ca2+-dependent protein binding in the cellular functions of ALG-2.

Palmitoylation of vacuole membrane protein 1 promotes small extracellular vesicle secretion via interaction with ALIX and influences intercellular communication

BACKGROUND

Small extracellular vesicles (EVs), exemplified by exosomes, mediate intercellular communication by transporting proteins, mRNAs, and miRNAs. Post-translational modifications are involved in controlling small EV secretion process. However, whether palmitoylation regulates small EV secretion, remains largely unexplored.

METHODS

Vacuole Membrane Protein 1 (VMP1) was testified to be S-palmitoylated by Palmitoylation assays. VMP1 mutant plasmids were constructed to screen out the exact palmitoylation sites. Small EVs were isolated, identified and compared between wild-type VMP1 or mutant VMP1 transfected cells. Electron microscope and immunofluorescence were used to detect multivesicular body (MVB) number and morphology change when VMP1 was mutated. Immunoprecipitation and Mass spectrum were adopted to identify the protein that interacted with palmitoylated VMP1, while knock down experiment was used to explore the function of targeted protein ALIX. Taking human Sertoli cells (SCs) and human spermatogonial stem cell like cells (SSCLCs) as a model of intercellular communication, SSCLC maintenance was detected by flow cytometry and qPCR at 12 days of differentiation. In vivo, mouse model was established by intraperitoneal injection with palmitoylation inhibitor, 2-bromopalmitate (2BP) for 3 months.

RESULTS

VMP1 was identified to be palmitoylated at cysteine 263,278 by ZDHHC3. Specifically, palmitoylation of VMP1 regulated its subcellular location and enhanced the amount of small EV secretion. Mutation of VMP1 palmitoylation sites interfered with the morphology and biogenesis of MVBs through suppressing intraluminal vesicle formation. Furthermore, inhibition of VMP1 palmitoylation impeded small EV secretion by affecting the interaction of VMP1 with ALIX, an accessory protein of the ESCRT machinery. Taking SCs and SSCLCs as a model of intercellular communication, we discovered VMP1 palmitoylation in SCs was vital to the growth status of SSCLCs in a co-culture system. Inhibition of VMP1 palmitoylation caused low self-maintenance, increased apoptosis, and decreased proliferation rate of SSCLCs. In vivo, intraperitoneal injection of 2BP inhibited VMP1 palmitoylation and exosomal marker expression in mouse testes, which were closely associated with the level of spermatogenic cell apoptosis and proliferation.

CONCLUSIONS

Our study revealed a novel mechanism for small EV secretion regulated by VMP1 palmitoylation in Sertoli cells, and demonstrated its pivotal role in intercellular communication and SSC niche.

A heterozygous germline deletion within USP8 causes severe neurodevelopmental delay with multiorgan abnormalities

Ubiquitin-specific protease 8 (USP8) is a deubiquitinating enzyme involved in deubiquitinating the enhanced epidermal growth factor receptor for escape from degradation. Somatic variants at a hotspot in USP8 are a cause of Cushing's disease, and a de novo germline USP8 variant at this hotspot has been described only once previously, in a girl with Cushing's disease and developmental delay. In this study, we investigated an exome-negative patient with severe developmental delay, dysmorphic features, and multiorgan dysfunction by long-read sequencing, and identified a 22-kb de novo germline deletion within USP8 (chr15:50469966-50491995 [GRCh38]). The deletion involved the variant hotspot, one rhodanese domain, and two SH3 binding motifs, and was presumed to be generated through nonallelic homologous recombination through Alu elements. Thus, the patient may have perturbation of the endosomal sorting system and mitochondrial autophagy through the USP8 defect. This is the second reported case of a germline variant in USP8.

High expression of VTA1 is an adverse prognostic factor in lung adenocarcinoma

Lung adenocarcinoma (LUAD) is a common pathological type of non-small cell lung cancer; identifying preferable biomarkers has become one of the current challenges. Given that VTA1 has been reported associated with tumor progression in various human solid cancers but rarely reported in LUAD, herein, RNA sequencing data from TCGA and GTEx were obtained for analysis of VTA1 expression and differentially expressed gene (DEG). Furthermore, functional enrichment analysis of VTA1-related DEGs was performed by GO/KEGG, GSEA, immune cell infiltration analysis, and protein-protein interaction (PPI) network. In addition, the clinical significance of VTA1 in LUAD was figured out by Kaplan-Meier Cox regression and prognostic nomogram model. R package was used to analyze incorporated studies. As a result, VTA1 was highly expressed in various malignancies, including LUAD, compared with normal samples. Moreover, high expression of VTA1 was associated with poor prognosis in 533 LUAD samples, as well as T stage T2&T3&T4, N stage N1&N2&N3, M stage M1, pathologic stage II&III&IV, and residual tumor R1&R2, et al. (P < 0.05). High VTA1 was an independent prognostic factor in Cox regression analysis; Age and cytogenetics risk were included in the nomogram prognostic model. Furthermore, a total of 4232 DEGs were identified between the high- and the low-expression group, of which 736 genes were up-regulated and 3496 genes were down-regulated. Collectively, high expression of VTA1 is a potential biomarker for adverse outcomes in LUAD. The DEGs and pathways recognized in the study provide a preliminary grasp of the underlying molecular mechanisms of LUAD carcinogenesis and progression.

CHMP3 promotes the progression of hepatocellular carcinoma by inhibiting caspase‑1‑dependent pyroptosis

Charged multivesicular body protein 3 (CHMP3) is an elemental constituent of the endosomal sorting complex required for transport (ESCRT) III, whose function as a tumor susceptibility gene in the development of liver cancer remains unclear. CHMP3 was found to be associated with pyroptosis by bioinformatics analysis of data from patients with hepatocellular carcinoma (HCC) in The Cancer Genome Atlas database. It was aimed to explore the role and potential mechanisms of CHMP3 in the development of liver cancer. The expression of CHMP3 at the tissue level was examined using immunohistochemistry and western blot analysis. Subsequently, HepG2 and Huh‑7 cells were transfected with small interfering RNA and overexpression plasmids to change CHMP3 expression. The proliferative capacity of cells was examined using colony formation and Cell Counting Kit‑8 assays. Wound healing and Transwell assays were used to examine the migratory and invasive abilities of the cells. Transmission electron microscopy was used to observe changes in cell morphology. Western blotting was used to examine the expression of caspase‑1 signaling pathway related proteins, a classic pathway of pyroptosis. In addition, a xenograft tumor model was used to examine the tumorigenic ability of CHMP3 in vivo. The results demonstrated that CHMP3 expression was upregulated in HCC and was associated with poor prognosis. Knockdown or overexpression of CHMP3 inhibited or promoted the proliferation, migration and invasion of liver cancer cells. Knockdown of Huh‑7 showed changes in cell membrane integrity as well as cytoplasmic leakage. Furthermore, knockdown of CHMP3 may activate the caspase‑1 pyroptosis signaling pathway which in turn inhibits the progression of liver cancer, and this effect can be reversed by the caspase‑1 inhibitor AYC. In conclusion, CHMP3 may affect the development of liver cancer through the caspase‑1‑mediated pyroptosis pathway.

Physiological Functions of the Ubiquitin Ligases Nedd4-1 and Nedd4-2

The Nedd4 family of E3 ubiquitin ligases, consisting of a C2-WW(n)-HECT domain architecture, includes the closely related Nedd4/Nedd4-1 and Nedd4L/Nedd4-2, which play critical roles in human physiology and pathophysiology.This review focuses on the regulation of enzymatic activity of these Nedd4 proteins, as well as on their roles in regulating stability and function of membrane and other signaling proteins, such as ion channels, ion transporters, and growth factor receptors. The diseases caused by impairment of such regulation are discussed, as well as opportunities and challenges for targeting these enzymes for therapy.

Expanding the spectrum of tyrosine kinase fusions in calcified chondroid mesenchymal neoplasms: Identification of a novel PDGFRA::USP8 gene fusion

Calcified chondroid mesenchymal neoplasms represent a distinct, and recently recognized, spectrum of tumors. To date most cases have been reported to be characterized by FN1 gene fusions involving multiple potential tyrosine kinase partners. Following incidental identification of a tumor morphologically corresponding to calcified chondroid mesenchymal neoplasm, but with a PDGFRA::USP8 gene fusion, we undertook a retrospective review to identify and characterize additional such cases. A total of four tumors were identified. Each was multilobulated and composed of polygonal-epithelioid-stellate cells with a background of chondroid matrix containing distinctive patterns of calcification. Targeted RNA sequencing revealed an identical PDGFRA (exon 22)::USP8 (exon 5) gene fusion in each case. Subsequent immunohistochemical staining confirmed the presence of PDGFRα overexpression. In summary, we report a series of four tumors within the morphologic spectrum of calcified chondroid mesenchymal neoplasms. In contrast to prior reports, these tumors harbored a novel PDGFRA::USP8 gene fusion, rather than FN1 rearrangement. Our findings expand the molecular diversity of these neoplasms, and suggest they are united through activation of protein kinases.

ATG and ESCRT control multiple modes of microautophagy

The discovery of microautophagy, the direct engulfment of cytoplasmic material by the lysosome, dates back to 1966 in a morphological study of mammalian cells by Christian de Duve. Since then, studies on microautophagy have shifted toward the elucidation of the physiological significance of the process. However, in contrast to macroautophagy, studies on the molecular mechanisms of microautophagy have been limited. Only recent studies revealed that ATG proteins involved in macroautophagy are also operative in several types of microautophagy and that ESCRT proteins, responsible for the multivesicular body pathway, play a central role in most microautophagy processes. In this review, we summarize our current knowledge on the function of ATG and ESCRT proteins in microautophagy.

ESCRT machinery and virus infection

The endosomal sorting complex required for transport (ESCRT) machinery plays a significant role in the spread of human viruses. However, our understanding of how the host ESCRT machinery responds to viral infection remains limited. Emerging evidence suggests that the ESCRT machinery can be hijacked by viruses of different families to enhance their replication. Throughout their life cycle, these viruses can interfere with or exploit ESCRT-mediated physiological processes to increase their chances of infecting the host. In contrast, to counteract virus infection, the interferon-stimulated gene 15 (ISG15) or the E3 ISG15-protein ligase (HERC5) system within the infected cells is activated to degrade the ESCRT proteins. Many retroviral and RNA viral proteins have evolved "late (L) domain" motifs, which enable them to recruit host ESCRT subunit proteins to facilitate virus transport, replication, budding, mature, and even endocytosis, Therefore, the L domain motifs and ESCRT subunit proteins could serve as promising drug targets for antiviral therapy. This review investigated the composition and essential functions of the ESCRT, shedding light on the impact of ESCRT subunits and viral L domain motifs on the replication of viruses. Furthermore, the antiviral effects facilitated by the ESCRT machinery have been investigated, aiming to provide valuable insights to guide the development and utilization of antiviral drugs.

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.

The role of midbody-associated mRNAs in regulating abscission

Midbodies function during telophase to regulate the abscission step of cytokinesis. Until recently, it was thought that abscission-regulating proteins, such as ESCRT-III complex subunits, accumulate at the MB by directly or indirectly binding to the MB resident protein, CEP55. However, recent studies have shown that depletion of CEP55 does not fully block ESCRT-III targeting the MB. Here, we show that MBs contain mRNAs and that these MB-associated mRNAs can be locally translated, resulting in the accumulation of abscission-regulating proteins. We demonstrate that localized MB-associated translation of CHMP4B is required for its targeting to the abscission site and that 3' UTR-dependent CHMP4B mRNA targeting to the MB is required for successful completion of cytokinesis. Finally, we identify regulatory cis-elements within RNAs that are necessary and sufficient for mRNA trafficking to the MB. We propose a novel method of regulating cytokinesis and abscission by MB-associated targeting and localized translation of selective mRNAs.

Clinical Spectrum of USP8 Pathogenic Variants in Cushing's Disease

Cushing's disease (CD) is a life-threatening condition with a challenging diagnostic process and scarce treatment options. CD is caused by usually benign adrenocorticotrophic hormone (ACTH)-secreting pituitary neuroendocrine tumors (PitNETs), known as corticotropinomas. These tumors are predominantly of sporadic origin, and usually derive from the monoclonal expansion of a mutated cell. Somatic activating variants located within a hotspot of the USP8 gene are present in 11-62% of corticotropinomas, making USP8 the most frequent genetic driver of corticotroph neoplasia. In contrast, other somatic defects such as those affecting the glucocorticoid receptor gene (NR3C1), the BRAF oncogene, the deubiquitinase-encoding gene USP48, and TP53 are infrequent. Moreover, patients with familial tumor syndromes, such as multiple endocrine neoplasia, familial isolated pituitary adenoma, and DICER1 rarely develop corticotropinomas. One of the main molecular alterations in USP8-driven tumors is an overactivation of the epidermal growth factor receptor (EGFR) signaling pathway, which induces ACTH production. Hotspot USP8 variants lead to persistent EGFR overexpression, thereby perpetuating the hyper-synthesis of ACTH. More importantly, they condition a characteristic transcriptomic signature that might be useful for the clinical prognosis of patients with CD. Nevertheless, the clinical phenotype associated with USP8 variants is less well defined. Hereby we discuss the current knowledge on the molecular pathogenesis and clinical picture associated with USP8 hotspot variants. We focus on the potential significance of the USP8 mutational status for the design of tailored clinical strategies in CD.

ESCRT-III Component CHMP4C Attenuates Cardiac Hypertrophy by Targeting the Endo-Lysosomal Degradation of EGFR

BACKGROUND

Cardiac hypertrophy and subsequent heart failure impose a considerable burden on public health worldwide. Impaired protein degradation, especially endo-lysosome-mediated degradation of membrane proteins, is associated with cardiac hypertrophy progression. CHMP4C (charged multivesicular body protein 4C), a critical constituent of multivesicular bodies, is involved in cellular trafficking and signaling. However, the specific role of CHMP4C in the progression of cardiac hypertrophy remains largely unknown.

METHODS

Mouse models with CHMP4C knockout or cardiadc-specific overexpression were subjected to transverse aortic constriction surgery for 4 weeks. Cardiac morphology and function were assessed through histological staining and echocardiography. Confocal imaging and coimmunoprecipitation assays were performed to identify the direct target of CHMP4C. An EGFR (epidermal growth factor receptor) inhibitor was administrated to determine whether effects of CHMP4C on cardiac hypertrophy were EGFR dependent.

RESULTS

CHMP4C was significantly upregulated in both pressure-overloaded mice and spontaneously hypertensive rats. Compared with wild-type mice, CHMP4C deficiency exacerbated transverse aortic constriction-induced cardiac hypertrophy, whereas CHMP4C overexpression in cardiomyocytes attenuated cardiac dysfunction. Mechanistically, the effect of CHMP4C on cardiac hypertrophy relied on the EGFR signaling pathway. Fluorescent staining and coimmunoprecipitation assays confirmed that CHMP4C interacts directly with EGFR and promotes lysosome-mediated degradation of activated EGFR, thus attenuating cardiac hypertrophy. Notably, an EGFR inhibitor canertinib counteracted the exacerbation of cardiac hypertrophy induced by CHMP4C knockdown in vitro and in vivo.

CONCLUSIONS

CHMP4C represses cardiac hypertrophy by modulating lysosomal degradation of EGFR and is a potential therapeutic candidate for cardiac hypertrophy.

Endosomal Arl4A attenuates EGFR degradation by binding to the ESCRT-II component VPS36

Ligand-induced epidermal growth factor receptor (EGFR) endocytosis followed by endosomal EGFR signaling and lysosomal degradation plays important roles in controlling multiple biological processes. ADP-ribosylation factor (Arf)-like protein 4 A (Arl4A) functions at the plasma membrane to mediate cytoskeletal remodeling and cell migration, whereas its localization at endosomal compartments remains functionally unknown. Here, we report that Arl4A attenuates EGFR degradation by binding to the endosomal sorting complex required for transport (ESCRT)-II component VPS36. Arl4A plays a role in prolonging the duration of EGFR ubiquitinylation and deterring endocytosed EGFR transport from endosomes to lysosomes under EGF stimulation. Mechanistically, the Arl4A-VPS36 direct interaction stabilizes VPS36 and ESCRT-III association, affecting subsequent recruitment of deubiquitinating-enzyme USP8 by CHMP2A. Impaired Arl4A-VPS36 interaction enhances EGFR degradation and clearance of EGFR ubiquitinylation. Together, we discover that Arl4A negatively regulates EGFR degradation by binding to VPS36 and attenuating ESCRT-mediated late endosomal EGFR sorting.

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.

ESCRT-dependent control of craniofacial morphogenesis with concomitant perturbation of NOTCH signaling

Craniofacial development is orchestrated by transcription factor-driven regulatory networks, epigenetic modifications, and signaling pathways. Signaling molecules and their receptors rely on endo-lysosomal trafficking to prevent accumulation on the plasma membrane. ESCRT (Endosomal Sorting Complexes Required for Transport) machinery is recruited to endosomal membranes enabling degradation of such endosomal cargoes. Studies in vitro and in invertebrate models established the requirements of the ESCRT machinery in membrane remodeling, endosomal trafficking, and lysosomal degradation of activated membrane receptors. However, investigations during vertebrate development have been scarce. By ENU-induced mutagenesis, we isolated a mouse line, Vps25ENU/ENU, carrying a hypomorphic allele of the ESCRT-II component Vps25, with craniofacial anomalies resembling features of human congenital syndromes. Here, we assessed the spatiotemporal dynamics of Vps25 and additional ESCRT-encoding genes during murine development. We show that these genes are ubiquitously expressed although enriched in discrete domains of the craniofacial complex, heart, and limbs. ESCRT-encoding genes, including Vps25, are expressed in both cranial neural crest-derived mesenchyme and epithelium. Unlike constitutive ESCRT mutants, Vps25ENU/ENU embryos display late lethality. They exhibit hypoplastic lower jaw, stunted snout, dysmorphic ear pinnae, and secondary palate clefting. Thus, we provide the first evidence for critical roles of ESCRT-II in craniofacial morphogenesis and report perturbation of NOTCH signaling in craniofacial domains of Vps25ENU/ENU embryos. Given the known roles of NOTCH signaling in the developing cranium, and notably the lower jaw, we propose that the NOTCH pathway partly mediates the craniofacial defects of Vps25ENU/ENU mouse embryos.

USP8 targeted by Mir-874-3p promotes trophoblastic cell invasion by stabilizing the expression of ENaC on trophoblast membrane

The aim of this study was to investigate the role of ubiquitin-specific peptidase 8 (USP8) in human trophoblast cells and its molecular mechanism. Based on the GSE30186 dataset, USP8 was identified as a downregulated gene in pre-eclampsia (PE). Analysis of clinical samples also revealed that USP8 expression at both the mRNA and protein levels in placental tissue from patients with PE was significantly lower than that from healthy pregnant women. Plate clone formation, scratch-wound healing, Transwell, tubule formation, and western blot assays collectively revealed that USP8 overexpression promoted the proliferation, migration, invasion, and pro-angiogenesis function of trophoblast cells, while USP8 knockdown induced the opposite effects. Bioinformatics analysis and luciferase reporter assay results indicated that the 3' untranslated region of USP8 was targeted by miR-874-3p. USP8 expression in the placental tissue of patients with PE was significantly lower than that of healthy pregnant women. USP8 actively regulated the growth and invasion of human trophoblast cells and stabilized the epithelial sodium channel (ENaC) on the cell membrane. MiR-874 targeted USP8 in the trophoblast cells and upregulation of miR-874-3p resulted in a decrease in the proliferation, migration, invasion, and pro-angiogenesis ability of trophoblast cells. These results indicate that USP8 can reverse the above mentioned negative effects of miR-874-3p on trophoblast cells. USP8 targeted by miR-874-3p facilitates the invasion of trophoblastic cells by stabilizing the expression of the ENaC, which may be a possible therapeutic target for PE.

[Virus hijacking ESCRT system to promote self-replication: a review]

Endosomal sorting complex required for transport (ESCRT) system drives various cellular processes, including endosome sorting, organelle biogenesis, vesicle transport, maintenance of plasma membrane integrity, membrane fission during cytokinesis, nuclear membrane reformation after mitosis, closure of autophagic vacuoles, and enveloped virus budding. Increasing evidence suggests that the ESCRT system can be hijacked by different family viruses for their proliferation. At different stages of the virus life cycle, viruses can interfere with or exploit ESCRT-mediated physiological processes in various ways to maximize their chance of infecting the host. In addition, many retroviral and RNA viral proteins possess "late domain" motifs, which can recruit host ESCRT subunit proteins to assist in virus endocytosis, transport, replicate, budding and efflux. Therefore, the "late domain" motifs of viruses and ESCRT subunit proteins could serve as promising drug targets in antiviral therapy. This review focuses on the composition and functions of the ESCRT system, the effects of ESCRT subunits and virus "late domain" motifs on viral replication, and the antiviral effects mediated by the ESCRT system, aiming to provide a reference for the development and utilization of antiviral drugs.

Primate-specific isoform of Nedd4-1 regulates substrate binding via Ser/Thr phosphorylation and 14-3-3 binding

Nedd4 (Nedd4-1) is an E3 ubiquitin ligase involved in crucial biological processes such as growth factor receptor signaling. While canonical Nedd4-1 comprises a C2-WW(4)-HECT domain architecture, alternative splicing produces non-canonical isoforms that are poorly characterized. Here we characterized Nedd4-1(NE), a primate-specific isoform of Nedd4-1 that contains a large N-terminal Extension (NE) that replaces most of the C2 domain. We show that Nedd4-1(NE) mRNA is ubiquitously expressed in human tissues and cell lines. Moreover, we found that Nedd4-1(NE) is more active than the canonical Nedd4-1 isoform, likely due to the absence of a C2 domain-mediated autoinhibitory mechanism. Additionally, we identified two Thr/Ser phosphoresidues in the NE region that act as binding sites for 14-3-3 proteins, and show that phosphorylation on these sites reduces substrate binding. Finally, we show that the NE region can act as a binding site for the RPB2 subunit of RNA polymerase II, a unique substrate of Nedd4-1(NE) but not the canonical Nedd4-1. Taken together, our results demonstrate that alternative splicing of the ubiquitin ligase Nedd4-1 can produce isoforms that differ in their catalytic activity, binding partners and substrates, and mechanisms of regulation.

Rab41-mediated ESCRT machinery repairs membrane rupture by a bacterial toxin in xenophagy

Xenophagy, a type of selective autophagy, is a bactericidal membrane trafficking that targets cytosolic bacterial pathogens, but the membrane homeostatic system to cope with bacterial infection in xenophagy is not known. Here, we show that the endosomal sorting complexes required for transport (ESCRT) machinery is needed to maintain homeostasis of xenophagolysosomes damaged by a bacterial toxin, which is regulated through the TOM1L2-Rab41 pathway that recruits AAA-ATPase VPS4. We screened Rab GTPases and identified Rab41 as critical for maintaining the acidification of xenophagolysosomes. Confocal microscopy revealed that ESCRT components were recruited to the entire xenophagolysosome, and this recruitment was inhibited by intrabody expression against bacterial cytolysin, indicating that ESCRT targets xenophagolysosomes in response to a bacterial toxin. Rab41 translocates to damaged autophagic membranes via adaptor protein TOM1L2 and recruits VPS4 to complete ESCRT-mediated membrane repair in a unique GTPase-independent manner. Finally, we demonstrate that the TOM1L2-Rab41 pathway-mediated ESCRT is critical for the efficient clearance of bacteria through xenophagy.

An ESCRT grommet cooperates with a diffusion barrier to maintain nuclear integrity

The molecular mechanisms by which the endosomal sorting complexes required for transport (ESCRT) proteins contribute to the integrity of the nuclear envelope (NE) barrier are not fully defined. We leveraged the single NE hole generated by mitotic extrusion of the Schizosaccharomyces pombe spindle pole body to reveal two modes of ESCRT function executed by distinct complements of ESCRT-III proteins, both dependent on CHMP7/Cmp7. A grommet-like function is required to restrict the NE hole in anaphase B, whereas replacement of Cmp7 by a sealing module ultimately closes the NE in interphase. Without Cmp7, nucleocytoplasmic compartmentalization remains intact despite NE discontinuities of up to 540 nm, suggesting mechanisms to limit diffusion through these holes. We implicate spindle pole body proteins as key components of a diffusion barrier acting with Cmp7 in anaphase B. Thus, NE remodelling mechanisms cooperate with proteinaceous diffusion barriers beyond nuclear pore complexes to maintain the nuclear compartment.

Nedd4-1 regulates human sodium-dependent vitamin C transporter-2 functional expression in neuronal and epithelial cells

The ubiquitin-proteasomal pathway regulates the functional expression of many membrane transporters in a variety of cellular systems. Nothing is currently known about the role of ubiquitin E3 ligase, neural precursor cell-expressed developmentally down-regulated gene 4 (Nedd4-1) and the proteasomal degradation pathway in regulating human vitamin C transporter-2 (hSVCT2) in neuronal cells. hSVCT2 mediates the uptake of ascorbic acid (AA) and is the predominantly expressed vitamin C transporter isoform in neuronal systems. Therefore, we addressed this knowledge gap in our study. Analysis of mRNA revealed markedly higher expression of Nedd4-1 in neuronal samples than that of Nedd4-2. Interestingly, Nedd4-1 expression in the hippocampus was higher in patients with Alzheimer's disease (AD) and age-dependently increased in the J20 mouse model of AD. The interaction of Nedd4-1 and hSVCT2 was confirmed by coimmunoprecipitation and colocalization. While the coexpression of Nedd4-1 with hSVCT2 displayed a significant decrease in AA uptake, siRNA-mediated knockdown of Nedd4-1 expression up-regulated the AA uptake. Further, we mutated a classical Nedd4 protein interacting motif ("PPXY") within the hSVCT2 polypeptide and observed markedly decreased AA uptake due to the intracellular localization of the mutated hSVCT2. Also, we determined the role of the proteasomal degradation pathway in hSVCT2 functional expression in SH-SY5Y cells and the results indicated that the proteasomal inhibitor (MG132) significantly up-regulated the AA uptake and hSVCT2 protein expression level. Taken together, our findings show that the regulation of hSVCT2 functional expression is at least partly mediated by the Nedd4-1 dependent ubiquitination and proteasomal pathways.

Nuclear pore complex and nucleocytoplasmic transport disruption in neurodegeneration

Nuclear pore complexes (NPCs) play a critical role in maintaining the equilibrium between the nucleus and cytoplasm, enabling bidirectional transport across the nuclear envelope, and are essential for proper nuclear organization and gene regulation. Perturbations in the regulatory mechanisms governing NPCs and nuclear envelope homeostasis have been implicated in the pathogenesis of several neurodegenerative diseases. The ESCRT-III pathway emerges as a critical player in the surveillance and preservation of well-assembled, functional NPCs, as well as nuclear envelope sealing. Recent studies have provided insights into the involvement of nuclear ESCRT-III in the selective reduction of specific nucleoporins associated with neurodegenerative pathologies. Thus, maintaining quality control of the nuclear envelope and NPCs represents a pivotal element in the pathological cascade leading to neurodegenerative diseases. This review describes the constituents of the nuclear-cytoplasmic transport machinery, encompassing the nuclear envelope, NPC, and ESCRT proteins, and how their structural and functional alterations contribute to the development of neurodegenerative diseases.

E3 ubiquitin ligase neural precursor cell-expressed developmentally downregulated gene 4 motivates FOXA1 ubiquitination and restrains proliferation of diffuse large B-cell lymphoma cells via the Wnt/β-Catenin pathway

Neural precursor cell-expressed developmentally downregulated gene 4 (NEDD4) is an E3 ubiquitin ligase that recognizes substrates via protein-protein interactions and takes part in tumor development. This study aims to clarify NEDD4's functions in diffuse large B-cell lymphoma (DLBCL) and its downstream mechanisms. Collection of 53 DLBCL tissues and adjacent normal lymphoid tissues, and detection of NEDD4 and Forkhead box protein A1 (FOXA1) in the tissues were conducted. The selection of DLBCL cells was for FARAGE, and test of cells' advancement was after transfection. Analysis of NEDD4 and FOXA1's link, and test of Wnt/β-catenin pathway were implemented. In vivo tumor xenograft experiments were put into effect. Detection of the pathological conditions of tumor tissues and the positive Ki67 in the family was implemented. It came out NEDD4 was reduced in DLBCL tissues and cell lines, and FOXA1 was elevated; Enhancing NEDD4 or repressing FOXA1 refrained DLBCL cells' advancement; NEDD4 could combine with FOXA1 and trigger its ubiquitination and degradation; NEDD4 inactivates the Wnt/β-catenin pathway by motivating FOXA1 ubiquitination; NEDD4 enhancement refrained DLBCL growth in vivo. In conclusion, the E3 ubiquitin ligase NEDD4 accelerates FOXA1 ubiquitination but refrains DLBCL cell proliferation via the Wnt/β-Catenin pathway.

Alteration of microglial metabolism and inflammatory profile contributes to neurotoxicity in a hiPSC-derived microglia model of frontotemporal dementia 3

Frontotemporal dementia (FTD) is a common cause of early-onset dementia, with no current treatment options. FTD linked to chromosome 3 (FTD3) is a rare sub-form of the disease, caused by a point mutation in the Charged Multivesicular Body Protein 2B (CHMP2B). This mutation causes neuronal phenotypes, such as mitochondrial deficiencies, accompanied by metabolic changes and interrupted endosomal-lysosomal fusion. However, the contribution of glial cells to FTD3 pathogenesis has, until recently, been largely unexplored. Glial cells play an important role in most neurodegenerative disorders as drivers and facilitators of neuroinflammation. Microglia are at the center of current investigations as potential pro-inflammatory drivers. While gliosis has been observed in FTD3 patient brains, it has not yet been systematically analyzed. In the light of this, we investigated the role of microglia in FTD3 by implementing human induced pluripotent stem cells (hiPSC) with either a heterozygous or homozygous CHMP2B mutation, introduced into a healthy control hiPSC line via CRISPR-Cas9 precision gene editing. These hiPSC were differentiated into microglia to evaluate the pro-inflammatory profile and metabolic state. Moreover, hiPSC-derived neurons were cultured with conditioned microglia media to investigate disease specific interactions between the two cell populations. Interestingly, we identified two divergent inflammatory microglial phenotypes resulting from the underlying mutations: a severe pro-inflammatory profile in CHMP2B homozygous FTD3 microglia, and an "unresponsive" CHMP2B heterozygous FTD3 microglial state. These findings correlate with our observations of increased phagocytic activity in CHMP2B homozygous, and impaired protein degradation in CHMP2B heterozygous FTD3 microglia. Metabolic mapping confirmed these differences, revealing a metabolic reprogramming of the CHMP2B FTD3 microglia, displayed as a compensatory up-regulation of glutamine metabolism in the CHMP2B homozygous FTD3 microglia. Intriguingly, conditioned CHMP2B homozygous FTD3 microglia media caused neurotoxic effects, which was not evident for the heterozygous microglia. Strikingly, IFN-γ treatment initiated an immune boost of the CHMP2B heterozygous FTD3 microglia, and conditioned microglia media exposure promoted neural outgrowth. Our findings indicate that the microglial profile, activity, and behavior is highly dependent on the status of the CHMP2B mutation. Our results suggest that the heterozygous state of the mutation in FTD3 patients could potentially be exploited in form of immune-boosting intervention strategies to counteract neurodegeneration.

UMAD1 contributes to ESCRT-III dynamic subunit turnover during cytokinetic abscission

Abscission is the final stage of cytokinesis whereby the midbody, a thin intercellular bridge, is resolved to separate the daughter cells. Cytokinetic abscission is mediated by the endosomal sorting complex required for transport (ESCRT), a conserved membrane remodelling machinery. The midbody organiser CEP55 recruits early acting ESCRT factors such as ESCRT-I and ALIX (also known as PDCD6IP), which subsequently initiate the formation of ESCRT-III polymers that sever the midbody. We now identify UMAD1 as an ESCRT-I subunit that facilitates abscission. UMAD1 selectively associates with VPS37C and VPS37B, supporting the formation of cytokinesis-specific ESCRT-I assemblies. TSG101 recruits UMAD1 to the site of midbody abscission, to stabilise the CEP55-ESCRT-I interaction. We further demonstrate that the UMAD1-ESCRT-I interaction facilitates the final step of cytokinesis. Paradoxically, UMAD1 and ALIX co-depletion has synergistic effects on abscission, whereas ESCRT-III recruitment to the midbody is not inhibited. Importantly, we find that both UMAD1 and ALIX are required for the dynamic exchange of ESCRT-III subunits at the midbody. Therefore, UMAD1 reveals a key functional connection between ESCRT-I and ESCRT-III that is required for cytokinesis.

miR-125b-5p impacts extracellular vesicle biogenesis, trafficking, and EV subpopulation release in the porcine trophoblast by regulating ESCRT-dependent pathway

Intercellular communication is a critical process that ensures cooperation between distinct cell types at the embryo-maternal interface. Extracellular vesicles (EVs) are considered to be potent mediators of this communication by transferring biological information in their cargo (e.g., miRNAs) to the recipient cells. miRNAs are small non-coding RNAs that affect the function and fate of neighboring and distant cells by regulating gene expression. Focusing on the maternal side of the dialog, we recently revealed the impact of embryonic signals, including miRNAs, on EV-mediated cell-to-cell communication. In this study, we show the regulatory mechanism of the miR-125b-5p ESCRT-mediated EV biogenesis pathway and the further secretion of EVs by trophoblasts at the time when the crucial steps of implantation are taking place. To test the ability of miR-125b-5p to influence the expression of genes involved in the generation and release of EV subpopulations in porcine conceptuses, we used an ex vivo approach. Next, in silico and in vitro analyses were performed to confirm miRNA-mRNA interactions. Finally, EV trafficking and release were assessed using several imaging and particle analysis tools. Our results indicated that conceptus development and implantation are accompanied by changes in the abundance of EV biogenesis and trafficking machinery. ESCRT-dependent EV biogenesis and the further secretion of EVs were modulated by miR-125b-5p, specifically impacting the ESCRT-II complex (via VPS36) and EV trafficking in primary porcine trophoblast cells. The identified miRNA-ESCRT interplay led to the generation and secretion of specific subpopulations of EVs. miRNA present at the embryo-maternal interface governs EV-mediated communication between the mother and the developing conceptus, leading to the generation, trafficking, and release of characteristic subpopulations of EVs.

A novel splice-site mutation in CHMP2B associated with frontotemporal dementia: The first report from China and literature review

BACKGROUND

Frontotemporal dementia (FTD) has genetic heterogeneity, and the endosomal ESCRTIII-complex subunit CHMP2B variant is a rare cause of FTD. The mutations in CHMP2B were first identified in a large Danish pedigree with autosomal dominant FTD, and have also been found in several individuals from Belgium, France, the United States, and Türkiye. In the Chinese population, cases of CHMP2B variant-associated FTD have never been reported.

METHODS

The spectrum of clinical symptoms and the genetic analysis of the presented patient were identified and investigated. Besides this case, we assessed previously reported cases with CHMP2B gene mutations.

RESULTS

This study presents a Chinese patient harboring a novel heterozygous A-to-T variant (NM_014043:c.532-2A>T) in CHMP2B with a phenotype compatible with FTD. Although previous reports suggested cases of CHMP2B variant-associated FTD initially presented with personality changes and stereotypical movements at the age of 50, this case was characterized by psychosis involving delusion of persecution, auditory hallucination, and suspiciousness at the earlier onset age of 44. Minigene splicing assay revealed that the splice-site variant could result in the retention of intron 5.

CONCLUSION

This is the first case of CHMP2B variant-associated FTD reported in the Chinese population. The novel c.532-2A>T variant in the acceptor splice site of exon 6 retaining intron 5 was predicted to cause truncated protein and protein conformation changes. This discovery may expand the genetic and phenotypic spectrum of CHMP2B variant-associated FTD.

Flattening out: A new ESCRT structure in cell adhesions

Conserved protein complexes called ESCRTs (endosomal sorting complexes in retrograde transport) exert diverse membrane remodeling and repair functions in cells. Hakala and Roux discuss a novel type of ESCRT-III structure found by Stempels et al. (2023. J. Cell Biol.https://doi.org/10.1083/jcb.202205130) in migrating macrophages and dendritic cells, suggesting a novel, cell type-specific function for this complex.

The maize ZmVPS23-like protein relocates the nucleotide-binding leucine-rich repeat protein Rp1-D21 to endosomes and suppresses the defense response

Plants often utilize nucleotide-binding leucine-rich repeat (NLR) proteins to perceive pathogen infections and trigger a hypersensitive response (HR). The endosomal sorting complex required for transport (ESCRT) machinery is a conserved multisubunit complex that is essential for the biogenesis of multivesicular bodies and cargo protein sorting. VPS23 is a key component of ESCRT-I and plays important roles in plant development and abiotic stresses. ZmVPS23L, a homolog of VPS23-like in maize (Zea mays), was previously identified as a candidate gene in modulating HR mediated by the autoactive NLR protein Rp1-D21 in different maize populations. Here, we demonstrate that ZmVPS23L suppresses Rp1-D21-mediated HR in maize and Nicotiana benthamiana. Variation in the suppressive effect of HR by different ZmVPS23L alleles was correlated with variation in their expression levels. ZmVPS23 also suppressed Rp1-D21-mediated HR. ZmVPS23L and ZmVPS23 predominantly localized to endosomes, and they physically interacted with the coiled-coil domain of Rp1-D21 and mediated the relocation of Rp1-D21 from the nucleo-cytoplasm to endosomes. In summary, we demonstrate that ZmVPS23L and ZmVPS23 are negative regulators of Rp1-D21-mediated HR, likely by sequestrating Rp1-D21 in endosomes via physical interaction. Our findings reveal the role of ESCRT components in controlling plant NLR-mediated defense responses.

Nuclear and cytoplasmic spatial protein quality control is coordinated by nuclear-vacuolar junctions and perinuclear ESCRT

Effective protein quality control (PQC), essential for cellular health, relies on spatial sequestration of misfolded proteins into defined inclusions. Here we reveal the coordination of nuclear and cytoplasmic spatial PQC. Cytoplasmic misfolded proteins concentrate in a cytoplasmic juxtanuclear quality control compartment, while nuclear misfolded proteins sequester into an intranuclear quality control compartment (INQ). Particle tracking reveals that INQ and the juxtanuclear quality control compartment converge to face each other across the nuclear envelope at a site proximal to the nuclear-vacuolar junction marked by perinuclear ESCRT-II/III protein Chm7. Strikingly, convergence at nuclear-vacuolar junction contacts facilitates VPS4-dependent vacuolar clearance of misfolded cytoplasmic and nuclear proteins, the latter entailing extrusion of nuclear INQ into the vacuole. Finding that nuclear-vacuolar contact sites are cellular hubs of spatial PQC to facilitate vacuolar clearance of nuclear and cytoplasmic inclusions highlights the role of cellular architecture in proteostasis maintenance.

USP8 inhibition regulates autophagy flux and controls Salmonella infection

Introduction

Ubiquitination is an important protein modification that regulates various essential cellular processes, including the functions of innate immune cells. Deubiquitinases are enzymes responsible for removing ubiquitin modification from substrates, and the regulation of deubiquitinases in macrophages during infection with Salmonella Typhimurium and Yersinia enterocolitica remains unknown.

Methods

To identify deubiquitinases regulated in human macrophages during bacterial infection, an activity-based proteomics screen was conducted. The effects of pharmacological inhibition of the identified deubiquitinase, USP8, were examined, including its impact on bacterial survival within macrophages and its role in autophagy regulation during Salmonella infection.

Results

Several deubiquiitnases were differentially regulated in infected macrophages. One of the deubiquitinases identified was USP8, which was downregulated upon Salmonella infection. Inhibition of USP8 was associated with a decrease in bacterial survival within macrophages, and it was found to play a distinct role in regulating autophagy during Salmonella infection. The inhibition of USP8 led to the downregulation of the p62 autophagy adaptor.

Discussion

The findings of this study suggest a novel role of USP8 in regulating autophagy flux, which restricts intracellular bacteria, particularly during Salmonella infection.

STING signalling is terminated through ESCRT-dependent microautophagy of vesicles originating from recycling endosomes

Stimulator of interferon genes (STING) is essential for the type I interferon response against a variety of DNA pathogens. Upon emergence of cytosolic DNA, STING translocates from the endoplasmic reticulum to the Golgi where STING activates the downstream kinase TBK1, then to lysosome through recycling endosomes (REs) for its degradation. Although the molecular machinery of STING activation is extensively studied and defined, the one underlying STING degradation and inactivation has not yet been fully elucidated. Here we show that STING is degraded by the endosomal sorting complexes required for transport (ESCRT)-driven microautophagy. Airyscan super-resolution microscopy and correlative light/electron microscopy suggest that STING-positive vesicles of an RE origin are directly encapsulated into Lamp1-positive compartments. Screening of mammalian Vps genes, the yeast homologues of which regulate Golgi-to-vacuole transport, shows that ESCRT proteins are essential for the STING encapsulation into Lamp1-positive compartments. Knockdown of Tsg101 and Vps4, components of ESCRT, results in the accumulation of STING vesicles in the cytosol, leading to the sustained type I interferon response. Knockdown of Tsg101 in human primary T cells leads to an increase the expression of interferon-stimulated genes. STING undergoes K63-linked ubiquitination at lysine 288 during its transit through the Golgi/REs, and this ubiquitination is required for STING degradation. Our results reveal a molecular mechanism that prevents hyperactivation of innate immune signalling, which operates at REs.

GPR143 controls ESCRT-dependent exosome biogenesis and promotes cancer metastasis

Exosomes transport a variety of macromolecules and modulate intercellular communication in physiology and disease. However, the regulation mechanisms that determine exosome contents during exosome biogenesis remain poorly understood. Here, we find that GPR143, an atypical GPCR, controls the endosomal sorting complex required for the transport (ESCRT)-dependent exosome biogenesis pathway. GPR143 interacts with HRS (an ESCRT-0 Subunit) and promotes its association to cargo proteins, such as EGFR, which subsequently enables selective protein sorting into intraluminal vesicles (ILVs) in multivesicular bodies (MVBs). GPR143 is elevated in multiple cancers, and quantitative proteomic and RNA profiling of exosomes in human cancer cell lines showed that the GPR143-ESCRT pathway promotes secretion of exosomes that carry unique cargo, including integrins signaling proteins. Through gain- and loss-of-function studies in mice, we show that GPR143 promotes metastasis by secreting exosomes and increasing cancer cell motility/invasion through the integrin/FAK/Src pathway. These findings provide a mechanism for regulating the exosomal proteome and demonstrate its ability to promote cancer cell motility.

ESCRT-dependent STING degradation inhibits steady-state and cGAMP-induced signalling

Stimulator of interferon genes (STING) is an intracellular sensor of cyclic di-nucleotides involved in the innate immune response against pathogen- or self-derived DNA. STING trafficking is tightly linked to its function, and its dysregulation can lead to disease. Here, we systematically characterize genes regulating STING trafficking and examine their impact on STING-mediated responses. Using proximity-ligation proteomics and genetic screens, we demonstrate that an endosomal sorting complex required for transport (ESCRT) complex containing HGS, VPS37A and UBAP1 promotes STING degradation, thereby terminating STING-mediated signaling. Mechanistically, STING oligomerization increases its ubiquitination by UBE2N, forming a platform for ESCRT recruitment at the endosome that terminates STING signaling via sorting in the lysosome. Finally, we show that expression of a UBAP1 mutant identified in patients with hereditary spastic paraplegia and associated with disrupted ESCRT function, increases steady-state STING-dependent type I IFN responses in healthy primary monocyte-derived dendritic cells and fibroblasts. Based on these findings, we propose that STING is subject to a tonic degradative flux and that the ESCRT complex acts as a homeostatic regulator of STING signaling.

Asgard ESCRT-III and VPS4 reveal conserved chromatin binding properties of the ESCRT machinery

The archaeal Asgard superphylum currently stands as the most promising prokaryotic candidate, from which eukaryotic cells emerged. This unique superphylum encodes for eukaryotic signature proteins (ESP) that could shed light on the origin of eukaryotes, but the properties and function of these proteins is largely unresolved. Here, we set to understand the function of an Asgard archaeal protein family, namely the ESCRT machinery, that is conserved across all domains of life and executes basic cellular eukaryotic functions, including membrane constriction during cell division. We find that ESCRT proteins encoded in Loki archaea, express in mammalian and yeast cells, and that the Loki ESCRT-III protein, CHMP4-7, resides in the eukaryotic nucleus in both organisms. Moreover, Loki ESCRT-III proteins associated with chromatin, recruited their AAA-ATPase VPS4 counterpart to organize in discrete foci in the mammalian nucleus, and directly bind DNA. The human ESCRT-III protein, CHMP1B, exhibited similar nuclear properties and recruited both human and Asgard VPS4s to nuclear foci, indicating interspecies interactions. Mutation analysis revealed a role for the N terminal region of ESCRT-III in mediating these phenotypes in both human and Asgard ESCRTs. These findings suggest that ESCRT proteins hold chromatin binding properties that were highly preserved through the billion years of evolution separating Asgard archaea and humans. The conserved chromatin binding properties of the ESCRT membrane remodeling machinery, reported here, may have important implications for the origin of eukaryogenesis.

The ESCRT-III Protein Chmp1 Regulates Lipid Storage in the Drosophila Fat Body

Defects in how excess nutrients are stored as triglycerides can result in several diseases including obesity, heart disease, and diabetes. Understanding the genes responsible for normal lipid homeostasis will help understand the pathogenesis of these diseases. RNAi screens performed in Drosophila cells identified genes involved in vesicle formation and protein sorting as important for the formation of lipid droplets; however, all of the vesicular trafficking proteins that regulate lipid storage are unknown. Here, we characterize the function of the Drosophila Charged multivesicular protein 1 (Chmp1) gene in regulating fat storage. Chmp1 is a member of the ESCRT-III complex that targets membrane localized signaling receptors to intralumenal vesicles in the multivesicular body of the endosome and then ultimately to the lysosome for degradation. When Chmp1 levels are decreased specifically in the fly fat body, triglyceride accumulates while fat-body-specific Chmp1 overexpression decreases triglycerides. Chmp1 controls triglyceride storage by regulating the number and size of fat body cells produced and not by altering food consumption or lipid metabolic enzyme gene expression. Together, these data uncover a novel function for Chmp1 in controlling lipid storage in Drosophila and supports the role of the endomembrane system in regulating metabolic homeostasis.