Moving and positioning the endolysosomal system

Structure of GDP-bound Rab7 Q67L in complex with ORP1L

Molecular processes are orchestrated by various proteins that promote early endosomes to become late endosomes and eventually fuse with lysosomes, guaranteeing the degradation of the content. Rab7, which is localized to late endosomes, is one of the most well-known GTPases. ORP1L is recruited by Rab7 to facilitate the fusion of late endosomes and lysosomes. Here, we present the structure of GDP-bound Rab7 Q67L with ORP1L. Structural analysis, supported by biochemical and ITC binding experiments, not only provides structural insight into the interactions between the ORP1L ANK domain and Rab7 but also suggests that the GTPase activity of Rab7 does not interfere with its ORP1L-binding capacity.

Lysosomal exocytosis: From cell protection to protumoral functions

Lysosomes are single membrane bounded group of acidic organelles that can be involved in a process called lysosomal exocytosis which leads to the extracellular release of their content. Lysosomal exocytosis is required for plasma membrane repair or remodeling events such as bone resorption, antigen presentation or mitosis, and for protection against toxic agents such as heavy metals. Recently, it has been showed that to fulfill this protective role, lysosomal exocytosis needs some autophagic proteins, in an autophagy-independent manner. In addition to these crucial physiological roles, lysosomal exocytosis plays a major protumoral role in various cancers. This effect is exerted through tumor microenvironment modifications, including extracellular matrix remodeling, acidosis, oncogenic and profibrogenic signals. This review provides a comprehensive overview of the different elements released in the microenvironment during lysosomal exocytosis, i.e. proteases, exosomes, and protons, and their effects in the context of tumor development and treatment.

Septin-coated microtubules promote maturation of multivesicular bodies by inhibiting their motility

The microtubule cytoskeleton consists of microtubule subsets with distinct compositions of microtubule-associated proteins, which instruct the position and traffic of subcellular organelles. In the endocytic pathway, these microtubule-associated cues are poorly understood. Here, we report that in MDCK cells, endosomes with multivesicular body (MVB) and late endosome (LE) markers localize preferentially to microtubules coated with septin GTPases. Compared with early endosomes, CD63-containing MVBs/LEs are largely immotile on septin-coated microtubules. In vitro reconstitution assays revealed that the motility of isolated GFP-CD63 endosomes is directly inhibited by microtubule-associated septins. Quantification of CD63-positive endosomes containing the early endosome antigen (EEA1), the Rab7 effector and dynein adaptor RILP or Rab27a, showed that intermediary EEA1- and RILP-positive GFP-CD63 preferentially associate with septin-coated microtubules. Septin knockdown enhanced GFP-CD63 motility and decreased the percentage of CD63-positive MVBs/LEs with lysobiphosphatidic acid without impacting the fraction of EEA1-positive CD63. These results suggest that MVB maturation involves immobilization on septin-coated microtubules, which may facilitate multivesiculation and/or organelle-organelle contacts.

Assembly and fission of tubular carriers mediating protein sorting in endosomes

Endosomes are central protein-sorting stations at the crossroads of numerous membrane trafficking pathways in all eukaryotes. They have a key role in protein homeostasis and cellular signalling and are involved in the pathogenesis of numerous diseases. Endosome-associated protein assemblies or coats collect transmembrane cargo proteins and concentrate them into retrieval domains. These domains can extend into tubular carriers, which then pinch off from the endosomal membrane and deliver the cargoes to appropriate subcellular compartments. Here we discuss novel insights into the structure of a number of tubular membrane coats that mediate the recruitment of cargoes into these carriers, focusing on sorting nexin-based coats such as Retromer, Commander and ESCPE-1. We summarize current and emerging views of how selective tubular endosomal carriers form and detach from endosomes by fission, highlighting structural aspects, conceptual challenges and open questions.

Lysosomal cholesterol accumulation in aged astrocytes impairs cholesterol delivery to neurons and can be rescued by cannabinoids

Cholesterol is crucial for the proper functioning of eukaryotic cells, especially neurons, which rely on cholesterol to maintain their complex structure and facilitate synaptic transmission. However, brain cells are isolated from peripheral cholesterol by the blood-brain barrier and mature neurons primarily uptake the cholesterol synthesized by astrocytes for proper function. This study aimed to investigate the effect of aging on cholesterol trafficking in astrocytes and its delivery to neurons. We found that aged astrocytes accumulated high levels of cholesterol in the lysosomal compartment, and this cholesterol buildup can be attributed to the simultaneous occurrence of two events: decreased levels of the ABCA1 transporter, which impairs ApoE-cholesterol export from astrocytes, and reduced expression of NPC1, which hinders cholesterol release from lysosomes. We show that these two events are accompanied by increased microR-33 in aged astrocytes, which targets ABCA1 and NPC1. In addition, we demonstrate that the microR-33 increase is triggered by oxidative stress, one of the hallmarks of aging. By coculture experiments, we show that cholesterol accumulation in astrocytes impairs the cholesterol delivery from astrocytes to neurons. Remarkably, we found that this altered transport of cholesterol could be alleviated through treatment with endocannabinoids as well as cannabidiol or CBD. Finally, according to data demonstrating that aged astrocytes develop an A1 phenotype, we found that cholesterol buildup is also observed in reactive C3+ astrocytes. Given that reduced neuronal cholesterol affects synaptic plasticity, the ability of cannabinoids to restore cholesterol transport from aged astrocytes to neurons holds significant implications in aging and inflammation.

The Drosophila Nesprin-1 homolog MSP300 is required for muscle autophagy and proteostasis

Nesprin proteins, which are components of the linker of nucleoskeleton and cytoskeleton (LINC) complex, are located within the nuclear envelope and play prominent roles in nuclear architecture. For example, LINC complex proteins interact with both chromatin and the cytoskeleton. Here, we report that the Drosophila Nesprin MSP300 has an additional function in autophagy within larval body wall muscles. RNAi-mediated MSP300 knockdown in larval body wall muscles resulted in defects in the contractile apparatus, muscle degeneration and defective autophagy. In particular, MSP300 knockdown caused accumulation of cytoplasmic aggregates that contained poly-ubiquitylated cargo, as well as the autophagy receptor ref(2)P (the fly homolog of p62 or SQSTM) and Atg8a. Furthermore, MSP300 knockdown larvae expressing an mCherry-GFP-tagged Atg8a transgene exhibited aberrant persistence of the GFP signal within these aggregates, indicating failure of autophagosome maturation. These autophagy deficits were similar to those exhibited by loss of the endoplasmic reticulum (ER) fusion protein Atlastin (Atl), raising the possibility that Atl and MSP300 might function in the same pathway. In support of this possibility, we found that a GFP-tagged MSP300 protein trap exhibited extensive localization to the ER. Alteration of ER-directed MSP300 might abrogate important cytoskeletal contacts necessary for autophagosome completion.

Movement of the endoplasmic reticulum is driven by multiple classes of vesicles marked by Rab-GTPases

Peripheral endoplasmic reticulum (ER) tubules move along microtubules to interact with various organelles through membrane contact sites (MCS). Traditionally, ER moves by either sliding along stable microtubules via molecular motors or attaching to the plus ends of dynamic microtubules through tip attachment complexes (TAC). A recently discovered third process, hitchhiking, involves motile vesicles pulling ER tubules along microtubules. Previous research showed that ER hitchhikes on Rab5- and Rab7-marked endosomes, but it is uncertain if other Rab-vesicles can do the same. In U2OS cells, we screened Rabs for their ability to cotransport with ER tubules and found that ER hitchhikes on post-Golgi vesicles marked by Rab6 (isoforms a and b). Rab6-ER hitchhiking occurs independently of ER-endolysosome contacts and TAC-mediated ER movement. Disrupting either Rab6 or the motility of Rab6-vesicles reduces overall ER movement. Conversely, relocating these vesicles to the cell periphery causes peripheral ER accumulation, indicating that Rab6-vesicle motility is crucial for a subset of ER movements. Proximal post-Golgi vesicles marked by TGN46 are involved in Rab6-ER hitchhiking, while other post-Golgi vesicles (Rabs 8/10/11/13/14) are not essential for ER movement. Our further analysis finds that ER to Golgi vesicles marked by Rab1 are also capable of driving a subset of ER movements. Taken together, our findings suggest that ER hitchhiking on Rab-vesicles is a significant mode of ER movement.

SIGNIFICANCE STATEMENT

Peripheral endoplasmic reticulum tubules move on microtubules by either attaching to motors (cargo adaptor-mediated), dynamic microtubule-plus ends (tip attachment complexes) or motile vesicles (hitchhiking) but the prevalence of each mode is not clearPost-Golgi vesicles marked by Rab6/TGN46 and ER to Golgi vesicles marked by Rab1 drive ER movementsER hitchhiking on multiple classes of vesicles (endolysosomal, post-Golgi and ER to Golgi) marked by Rabs plays a prominent role in ER movement.

Lysosomes in Cancer-At the Crossroad of Good and Evil

Although it has been known for decades that lysosomes are central for degradation and recycling in the cell, their pivotal role as nutrient sensing signaling hubs has recently become of central interest. Since lysosomes are highly dynamic and in constant change regarding content and intracellular position, fusion/fission events allow communication between organelles in the cell, as well as cell-to-cell communication via exocytosis of lysosomal content and release of extracellular vesicles. Lysosomes also mediate different forms of regulated cell death by permeabilization of the lysosomal membrane and release of their content to the cytosol. In cancer cells, lysosomal biogenesis and autophagy are increased to support the increased metabolism and allow growth even under nutrient- and oxygen-poor conditions. Tumor cells also induce exocytosis of lysosomal content to the extracellular space to promote invasion and metastasis. However, due to the enhanced lysosomal function, cancer cells are often more susceptible to lysosomal membrane permeabilization, providing an alternative strategy to induce cell death. This review summarizes the current knowledge of cancer-associated alterations in lysosomal structure and function and illustrates how lysosomal exocytosis and release of extracellular vesicles affect disease progression. We focus on functional differences depending on lysosomal localization and the regulation of intracellular transport, and lastly provide insight how new therapeutic strategies can exploit the power of the lysosome and improve cancer treatment.

Endolysosomal vesicles at the center of B cell activation

The endolysosomal system specializes in degrading cellular components and is crucial to maintaining homeostasis and adapting rapidly to metabolic and environmental cues. Cells of the immune system exploit this network to process antigens or promote cell death by secreting lysosome-related vesicles. In B lymphocytes, lysosomes are harnessed to facilitate the extraction of antigens and to promote their processing into peptides for presentation to T cells, critical steps to mount protective high-affinity antibody responses. Intriguingly, lysosomal vesicles are now considered important signaling units within cells and also display secretory functions by releasing their content to the extracellular space. In this review, we focus on how B cells use pathways involved in the intracellular trafficking, secretion, and function of endolysosomes to promote adaptive immune responses. A basic understanding of such mechanisms poses an interesting frontier for the development of therapeutic strategies in the context of cancer and autoimmune diseases.

Lysosomes as coordinators of cellular catabolism, metabolic signalling and organ physiology

Every cell must satisfy basic requirements for nutrient sensing, utilization and recycling through macromolecular breakdown to coordinate programmes for growth, repair and stress adaptation. The lysosome orchestrates these key functions through the synchronised interplay between hydrolytic enzymes, nutrient transporters and signalling factors, which together enable metabolic coordination with other organelles and regulation of specific gene expression programmes. In this Review, we discuss recent findings on lysosome-dependent signalling pathways, focusing on how the lysosome senses nutrient availability through its physical and functional association with mechanistic target of rapamycin complex 1 (mTORC1) and how, in response, the microphthalmia/transcription factor E (MiT/TFE) transcription factors exert feedback regulation on lysosome biogenesis. We also highlight the emerging interactions of lysosomes with other organelles, which contribute to cellular homeostasis. Lastly, we discuss how lysosome dysfunction contributes to diverse disease pathologies and how inherited mutations that compromise lysosomal hydrolysis, transport or signalling components lead to multi-organ disorders with severe metabolic and neurological impact. A deeper comprehension of lysosomal composition and function, at both the cellular and organismal level, may uncover fundamental insights into human physiology and disease.

Intracellular trafficking of HIV-1 Gag via Syntaxin 6-positive compartments/vesicles: Involvement in tumor necrosis factor secretion

HIV-1 Gag protein is synthesized in the cytosol and is transported to the plasma membrane, where viral particle assembly and budding occur. Endosomes are alternative sites of Gag accumulation. However, the intracellular transport pathways and carriers for Gag have not been clarified. We show here that Syntaxin6 (Syx6), a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) involved in membrane fusion in post-Golgi networks, is a molecule responsible for Gag trafficking and also for tumor necrosis factor-α (TNFα) secretion and that Gag and TNFα are cotransported via Syx6-positive compartments/vesicles. Confocal and live-cell imaging revealed that Gag colocalized and cotrafficked with Syx6, a fraction of which localizes in early and recycling endosomes. Syx6 knockdown reduced HIV-1 particle production, with Gag distributed diffusely throughout the cytoplasm. Coimmunoprecipitation and pulldown show that Gag binds to Syx6, but not its SNARE partners or their assembly complexes, suggesting that Gag preferentially binds free Syx6. The Gag matrix domain and the Syx6 SNARE domain are responsible for the interaction and cotrafficking. In immune cells, Syx6 knockdown/knockout similarly impaired HIV-1 production. Interestingly, HIV-1 infection facilitated TNFα secretion, and this enhancement did not occur in Syx6-depleted cells. Confocal and live-cell imaging revealed that TNFα and Gag partially colocalized and were cotransported via Syx6-positive compartments/vesicles. Biochemical analyses indicate that TNFα directly binds the C-terminal domain of Syx6. Altogether, our data provide evidence that both Gag and TNFα make use of Syx6-mediated trafficking machinery and suggest that Gag expression does not inhibit but rather facilitates TNFα secretion in HIV-1 infection.

Phosphoglycerate kinase 1 acts as a cargo adaptor to promote EGFR transport to the lysosome

The epidermal growth factor receptor (EGFR) plays important roles in multiple cellular events, including growth, differentiation, and motility. A major mechanism of downregulating EGFR function involves its endocytic transport to the lysosome. Sorting of proteins into intracellular pathways involves cargo adaptors recognizing sorting signals on cargo proteins. A dileucine-based sorting signal has been identified previously for the sorting of endosomal EGFR to the lysosome, but a cargo adaptor that recognizes this signal remains unknown. Here, we find that phosphoglycerate kinase 1 (PGK1) is recruited to endosomal membrane upon its phosphorylation, where it binds to the dileucine sorting signal in EGFR to promote the lysosomal transport of this receptor. We also elucidate two mechanisms that act in concert to promote PGK1 recruitment to endosomal membrane, a lipid-based mechanism that involves phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] and a protein-based mechanism that involves hepatocyte growth factor receptor substrate (Hrs). These findings reveal an unexpected function for a metabolic enzyme and advance the mechanistic understanding of how EGFR is transported to the lysosome.

DENND6A links Arl8b to a Rab34/RILP/dynein complex, regulating lysosomal positioning and autophagy

Lysosomes help maintain cellular proteostasis, and defects in lysosomal positioning and function can cause disease, including neurodegenerative disorders. The spatiotemporal distribution of lysosomes is regulated by small GTPases including Rabs, which are activated by guanine nucleotide exchange factors (GEFs). DENN domain proteins are the largest family of Rab GEFs. Using a cell-based assay, we screened DENND6A, a member of the DENN domain protein family against all known Rabs and identified it as a potential GEF for 20 Rabs, including Rab34. Here, we demonstrate that DENND6A activates Rab34, which recruits a RILP/dynein complex to lysosomes, promoting lysosome retrograde transport. Further, we identify DENND6A as an effector of Arl8b, a major regulatory GTPase on lysosomes. We demonstrate that Arl8b recruits DENND6A to peripheral lysosomes to activate Rab34 and initiate retrograde transport, regulating nutrient-dependent lysosomal juxtanuclear repositioning. Loss of DENND6A impairs autophagic flux. Our findings support a model whereby Arl8b/DENND6A/Rab34-dependent lysosomal retrograde trafficking controls autophagy.

Making the connection: How membrane contact sites have changed our view of organelle biology

The view of organelles and how they operate together has changed dramatically over the last two decades. The textbook view of organelles was that they operated largely independently and were connected by vesicular trafficking and the diffusion of signals through the cytoplasm. We now know that all organelles make functional close contacts with one another, often called membrane contact sites. The study of these sites has moved to center stage in cell biology as it has become clear that they play critical roles in healthy and developing cells and during cell stress and disease states. Contact sites have important roles in intracellular signaling, lipid metabolism, motor-protein-mediated membrane dynamics, organelle division, and organelle biogenesis. Here, we summarize the major conceptual changes that have occurred in cell biology as we have come to appreciate how contact sites integrate the activities of organelles.

Lysosomal dynamics regulate mammalian cortical neurogenesis

Mammalian neocortex formation follows a stereotypical pattern wherein the self-renew and differentiation of neural stem cells are coordinated with diverse organelle dynamics. However, the role of lysosomes in brain development has long been overlooked. Here, we demonstrate the highly dynamic lysosomal quantities, types, and localizations in developing brain. We observed asymmetric endolysosome inheritance during radial glial cell (RGC) division and the increased autolysosomes within intermediate progenitor cells (IPs) and newborn neurons. Disruption of lysosomal function shortens the S phase of the cell cycle and promotes RGC differentiation. Mechanistically, we revealed a post-transcriptional regulation governing ribosome homeostasis and cell-cycle progression through differential lysosomal activity modulation. In the human forebrain organoid, lysosomal dynamics are conserved; specifically, during the mitosis of outer subventricular zone RGCs (oRGs), lysosomes are inherited by the progeny without basal process. Together, our results identify the critical role of lysosomal dynamics in regulating mouse and human brain development.

TMEM55B links autophagy flux, lysosomal repair, and TFE3 activation in response to oxidative stress

Lysosomes have emerged as critical regulators of cellular homeostasis. Here we show that the lysosomal protein TMEM55B contributes to restore cellular homeostasis in response to oxidative stress by three different mechanisms: (1) TMEM55B mediates NEDD4-dependent PLEKHM1 ubiquitination, causing PLEKHM1 proteasomal degradation and halting autophagosome/lysosome fusion; (2) TMEM55B promotes recruitment of components of the ESCRT machinery to lysosomal membranes to stimulate lysosomal repair; and (3) TMEM55B sequesters the FLCN/FNIP complex to facilitate translocation of the transcription factor TFE3 to the nucleus, allowing expression of transcriptional programs that enable cellular adaptation to stress. Knockout of tmem55 genes in zebrafish embryos increases their susceptibility to oxidative stress, causing early death of tmem55-KO animals in response to arsenite toxicity. Altogether, our work identifies a role for TMEM55B as a molecular sensor that coordinates autophagosome degradation, lysosomal repair, and activation of stress responses.

Passive diffusion accounts for the majority of intracellular nanovesicle transport

During membrane trafficking, a vesicle formed at the donor compartment must travel to the acceptor membrane before fusing. For large carriers, it is established that this transport is motor-driven; however, the mode by which small vesicles, which outnumber larger carriers, are transported is poorly characterized. Here, we show that intracellular nanovesicles (INVs), a substantial class of small vesicles, are highly mobile within cells and that this mobility depends almost entirely on passive diffusion (0.1-0.3 μm2 s-1). Using single particle tracking, we describe how other small trafficking vesicles have a similar diffusive mode of transport that contrasts with the motor-dependent movement of larger endolysosomal carriers. We also demonstrate that a subset of INVs is involved in exocytosis and that delivery of cargo to the plasma membrane during exocytosis is decreased when diffusion of INVs is specifically restricted. Our results suggest that passive diffusion is sufficient to explain the majority of small vesicle transport.

Spatacsin regulates directionality of lysosome trafficking by promoting the degradation of its partner AP5Z1

The endoplasmic reticulum (ER) forms contacts with the lysosomal compartment, regulating lysosome positioning and motility. The movements of lysosomes are controlled by the attachment of molecular motors to their surface. However, the molecular mechanisms by which ER controls lysosome dynamics are still elusive. Here, using mouse brain extracts and mouse embryonic fibroblasts, we demonstrate that spatacsin is an ER-resident protein regulating the formation of tubular lysosomes, which are highly dynamic. Screening for spatacsin partners required for tubular lysosome formation showed spatacsin to act by regulating protein degradation. We demonstrate that spatacsin promotes the degradation of its partner AP5Z1, which regulates the relative amount of spastizin and AP5Z1 at lysosomes. Spastizin and AP5Z1 contribute to regulate tubular lysosome formation, as well as their trafficking by interacting with anterograde and retrograde motor proteins, kinesin KIF13A and dynein/dynactin subunit p150Glued, respectively. Ultimately, investigations in polarized mouse cortical neurons in culture demonstrated that spatacsin-regulated degradation of AP5Z1 controls the directionality of lysosomes trafficking. Collectively, our results identify spatacsin as a protein regulating the directionality of lysosome trafficking.

Presynaptic Precursor Vesicles-Cargo, Biogenesis, and Kinesin-Based Transport across Species

The faithful formation and, consequently, function of a synapse requires continuous and tightly controlled delivery of synaptic material. At the presynapse, a variety of proteins with unequal molecular properties are indispensable to compose and control the molecular machinery concerting neurotransmitter release through synaptic vesicle fusion with the presynaptic membrane. As presynaptic proteins are produced mainly in the neuronal soma, they are obliged to traffic along microtubules through the axon to reach the consuming presynapse. This anterograde transport is performed by highly specialised and diverse presynaptic precursor vesicles, membranous organelles able to transport as different proteins such as synaptic vesicle membrane and membrane-associated proteins, cytosolic active zone proteins, ion-channels, and presynaptic membrane proteins, coordinating synaptic vesicle exo- and endocytosis. This review aims to summarise and categorise the diverse and numerous findings describing presynaptic precursor cargo, mode of trafficking, kinesin-based axonal transport and the molecular mechanisms of presynaptic precursor vesicles biogenesis in both vertebrate and invertebrate model systems.

Lysosomal Function and Intracellular Position Determine the Malignant Phenotype in Malignant Melanoma

Lysosomes are central in cell homeostasis and participate in macromolecular degradation, plasma membrane repair, exosome release, cell adhesion/migration, and apoptosis. In cancer, alterations in lysosomal function and spatial distribution may facilitate disease progression. In this study, we show enhanced lysosomal activity in malignant melanoma cells compared with that in normal human melanocytes. Most lysosomes show perinuclear location in melanocytes, while they are more dispersed in melanoma, with retained proteolytic activity and low pH also in the peripheral population. Rab7a expression is lower in melanoma cells than in melanocytes, and by increasing Rab7a, lysosomes are relocated to the perinuclear region in melanoma. Exposure to the lysosome-destabilizing drug L-leucyl-L-leucine methyl ester causes higher damage in the perinuclear subset of lysosomes in melanomas, whereas differences in subpopulation susceptibility cannot be found in melanocytes. Interestingly, melanoma cells recruit the endosomal sorting complex required for transport-III core protein CHMP4B, involved in lysosomal membrane repair, rather than initiate lysophagy. However, when the perinuclear lysosomal position is promoted by Rab7a overexpression or kinesore treatment, lysophagy is increased. In addition, Rab7a overexpression is accompanied by reduced migration capacity. Taken together, the study emphasizes that alterations in lysosomal properties facilitate the malignant phenotype and declares the targeting of lysosomal function as a future therapeutic approach.

Endoplasmic reticulum membrane contact sites: cross-talk between membrane-bound organelles in plant cells

Eukaryotic cells contain organelles surrounded by monolayer or bilayer membranes. Organelles take part in highly dynamic and organized interactions at membrane contact sites, which play vital roles during development and response to stress. The endoplasmic reticulum extends throughout the cell and acts as an architectural scaffold to maintain the spatial distribution of other membrane-bound organelles. In this review, we highlight the structural organization, dynamics, and physiological functions of membrane contact sites between the endoplasmic reticulum and various membrane-bound organelles, especially recent advances in plants. We briefly introduce how the combined use of dynamic and static imaging techniques can enable monitoring of the cross-talk between organelles via membrane contact sites. Finally, we discuss future directions for research fields related to membrane contact.

Elucidation of the Cellular Interactome of African Swine Fever Virus Fusion Proteins and Identification of Potential Therapeutic Targets

African swine fever virus (ASFV) encodes more than 150 proteins, most of them of unknown function. We used a high-throughput proteomic analysis to elucidate the interactome of four ASFV proteins, which potentially mediate a critical step of the infection cycle, the fusion and endosomal exit of the virions. Using affinity purification and mass spectrometry, we were able to identify potential interacting partners for those ASFV proteins P34, E199L, MGF360-15R and E248R. Representative molecular pathways for these proteins were intracellular and Golgi vesicle transport, endoplasmic reticulum organization, lipid biosynthesis, and cholesterol metabolism. Rab geranyl geranylation emerged as a significant hit, and also Rab proteins, which are crucial regulators of the endocytic pathway and interactors of both p34 and E199L. Rab proteins co-ordinate a tight regulation of the endocytic pathway that is necessary for ASFV infection. Moreover, several interactors were proteins involved in the molecular exchange at ER membrane contacts. These ASFV fusion proteins shared interacting partners, suggesting potential common functions. Membrane trafficking and lipid metabolism were important categories, as we found significant interactions with several enzymes of the lipid metabolism. These targets were confirmed using specific inhibitors with antiviral effect in cell lines and macrophages.

Palmitate-mediated disruption of the endoplasmic reticulum decreases intracellular vesicle motility

Essential cellular processes such as metabolism, protein synthesis, and autophagy require the intracellular transport of membrane-bound vesicles. The importance of the cytoskeleton and associated molecular motors for transport is well documented. Recent research has suggested that the endoplasmic reticulum (ER) may also play a role in vesicle transport through a tethering of vesicles to the ER. We use single-particle tracking fluorescence microscopy and a Bayesian change-point algorithm to characterize vesicle motility in response to the disruption of the ER, actin, and microtubules. This high-throughput change-point algorithm allows us to efficiently analyze thousands of trajectory segments. We find that palmitate-mediated disruption of the ER leads to a significant decrease in vesicle motility. A comparison with the disruption of actin and microtubules shows that disruption of the ER has a significant impact on vesicle motility, greater than the disruption of actin. Vesicle motility was dependent on cellular region, with greater motility in the cell periphery than the perinuclear region, possibly due to regional differences in actin and the ER. Overall, these results suggest that the ER is an important factor in vesicle transport.

Enhancing the Effectiveness of Oligonucleotide Therapeutics Using Cell-Penetrating Peptide Conjugation, Chemical Modification, and Carrier-Based Delivery Strategies

Oligonucleotide-based therapies are a promising approach for treating a wide range of hard-to-treat diseases, particularly genetic and rare diseases. These therapies involve the use of short synthetic sequences of DNA or RNA that can modulate gene expression or inhibit proteins through various mechanisms. Despite the potential of these therapies, a significant barrier to their widespread use is the difficulty in ensuring their uptake by target cells/tissues. Strategies to overcome this challenge include cell-penetrating peptide conjugation, chemical modification, nanoparticle formulation, and the use of endogenous vesicles, spherical nucleic acids, and smart material-based delivery vehicles. This article provides an overview of these strategies and their potential for the efficient delivery of oligonucleotide drugs, as well as the safety and toxicity considerations, regulatory requirements, and challenges in translating these therapies from the laboratory to the clinic.

Secretion of VGF relies on the interplay between LRRK2 and post-Golgi v-SNAREs

The neuropeptide VGF was recently proposed as a neurodegeneration biomarker. The Parkinson's disease-related protein leucine-rich repeat kinase 2 (LRRK2) regulates endolysosomal dynamics, a process that involves SNARE-mediated membrane fusion and could regulate secretion. Here we investigate potential biochemical and functional links between LRRK2 and v-SNAREs. We find that LRRK2 directly interacts with the v-SNAREs VAMP4 and VAMP7. Secretomics reveals VGF secretory defects in VAMP4 and VAMP7 knockout (KO) neuronal cells. In contrast, VAMP2 KO "regulated secretion-null" and ATG5 KO "autophagy-null" cells release more VGF. VGF is partially associated with extracellular vesicles and LAMP1+ endolysosomes. LRRK2 expression increases VGF perinuclear localization and impairs its secretion. Retention using selective hooks (RUSH) assays show that a pool of VGF traffics through VAMP4+ and VAMP7+ compartments, and LRRK2 expression delays its transport to the cell periphery. Overexpression of LRRK2 or VAMP7-longin domain impairs VGF peripheral localization in primary cultured neurons. Altogether, our results suggest that LRRK2 might regulate VGF secretion via interaction with VAMP4 and VAMP7.

The role of lysosomes in metabolic and autoimmune diseases

Lysosomes are catabolic organelles that contribute to the degradation of intracellular constituents through autophagy and of extracellular components through endocytosis, phagocytosis and macropinocytosis. They also have roles in secretory mechanisms, the generation of extracellular vesicles and certain cell death pathways. These functions make lysosomes central organelles in cell homeostasis, metabolic regulation and responses to environment changes including nutrient stresses, endoplasmic reticulum stress and defects in proteostasis. Lysosomes also have important roles in inflammation, antigen presentation and the maintenance of long-lived immune cells. Their functions are tightly regulated by transcriptional modulation via TFEB and TFE3, as well as by major signalling pathways that lead to activation of mTORC1 and mTORC2, lysosome motility and fusion with other compartments. Lysosome dysfunction and alterations in autophagy processes have been identified in a wide variety of diseases, including autoimmune, metabolic and kidney diseases. Deregulation of autophagy can contribute to inflammation, and lysosomal defects in immune cells and/or kidney cells have been reported in inflammatory and autoimmune pathologies with kidney involvement. Defects in lysosomal activity have also been identified in several pathologies with disturbances in proteostasis, including autoimmune and metabolic diseases such as Parkinson disease, diabetes mellitus and lysosomal storage diseases. Targeting lysosomes is therefore a potential therapeutic strategy to regulate inflammation and metabolism in a variety of pathologies.

Lysosome signaling in cell survival and programmed cell death for cellular homeostasis

Recent developments in lysosome biology have transformed our view of lysosomes from static garbage disposals that can also act as suicide bags to decidedly dynamic multirole adaptive operators of cellular homeostasis. Lysosome-governed signaling pathways, proteins, and transcription factors equilibrate the rate of catabolism and anabolism (autophagy to lysosomal biogenesis and metabolite pool maintenance) by sensing cellular metabolic status. Lysosomes also interact with other organelles by establishing contact sites through which they exchange cellular contents. Lysosomal function is critically assessed by lysosomal positioning and motility for cellular adaptation. In this setting, mechanistic target of rapamycin kinase (MTOR) is the chief architect of lysosomal signaling to control cellular homeostasis. Notably, lysosomes can orchestrate explicit cell death mechanisms, such as autophagic cell death and lysosomal membrane permeabilization-associated regulated necrotic cell death, to maintain cellular homeostasis. These lines of evidence emphasize that the lysosomes serve as a central signaling hub for cellular homeostasis.

Molecular machinery regulating organelle dynamics during axon growth and guidance

Axon growth and guidance in the developing nervous system rely on intracellular membrane dynamics that involve endosome maturation and transport, as well as its regulated tethering to the endoplasmic reticulum (ER). Recent studies have identified several key molecules, such as protrudin, which plays a dynamic role at membrane contact sites between the ER and endosomes/lysosomes, and myosin Va, which acts as a sensor for ER-derived Ca²⁺ that triggers peri-ER membrane export. These molecules form different types of multiprotein complexes at the interface of organelles and, in response to their surrounding microenvironments, such as Ca²⁺ concentrations and lipid contents, regulate the directional movement of endosomal vesicles in extending axons. Here, we review the molecular mechanisms underlying membrane dynamics and inter-organelle interactions during neuronal morphogenesis.

Ca2+ and Annexins - Emerging Players for Sensing and Transferring Cholesterol and Phosphoinositides via Membrane Contact Sites

Maintaining lipid composition diversity in membranes from different organelles is critical for numerous cellular processes. However, many lipids are synthesized in the endoplasmic reticulum (ER) and require delivery to other organelles. In this scenario, formation of membrane contact sites (MCS) between neighbouring organelles has emerged as a novel non-vesicular lipid transport mechanism. Dissecting the molecular composition of MCS identified phosphoinositides (PIs), cholesterol, scaffolding/tethering proteins as well as Ca²⁺ and Ca²⁺-binding proteins contributing to MCS functioning. Compelling evidence now exists for the shuttling of PIs and cholesterol across MCS, affecting their concentrations in distinct membrane domains and diverse roles in membrane trafficking. Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) at the plasma membrane (PM) not only controls endo-/exocytic membrane dynamics but is also critical in autophagy. Cholesterol is highly concentrated at the PM and enriched in recycling endosomes and Golgi membranes. MCS-mediated cholesterol transfer is intensely researched, identifying MCS dysfunction or altered MCS partnerships to correlate with de-regulated cellular cholesterol homeostasis and pathologies. Annexins, a conserved family of Ca²⁺-dependent phospholipid binding proteins, contribute to tethering and untethering events at MCS. In this chapter, we will discuss how Ca²⁺ homeostasis and annexins in the endocytic compartment affect the sensing and transfer of cholesterol and PIs across MCS.

Structural basis for Parkinson's disease-linked LRRK2's binding to microtubules

Leucine-rich repeat kinase 2 (LRRK2) is one of the most commonly mutated genes in familial Parkinson's disease (PD). Under some circumstances, LRRK2 co-localizes with microtubules in cells, an association enhanced by PD mutations. We report a cryo-EM structure of the catalytic half of LRRK2, containing its kinase, in a closed conformation, and GTPase domains, bound to microtubules. We also report a structure of the catalytic half of LRRK1, which is closely related to LRRK2 but is not linked to PD. Although LRRK1's structure is similar to that of LRRK2, we find that LRRK1 does not interact with microtubules. Guided by these structures, we identify amino acids in LRRK2's GTPase that mediate microtubule binding; mutating them disrupts microtubule binding in vitro and in cells, without affecting LRRK2's kinase activity. Our results have implications for the design of therapeutic LRRK2 kinase inhibitors.

Choreographing the motor-driven endosomal dance

The endosomal system orchestrates the transport of lipids, proteins and nutrients across the entire cell. Along their journey, endosomes mature, change shape via fusion and fission, and communicate with other organelles. This intriguing endosomal choreography, which includes bidirectional and stop-and-go motions, is coordinated by the microtubule-based motor proteins dynein and kinesin. These motors bridge various endosomal subtypes to the microtubule tracks thanks to their cargo-binding domain interacting with endosome-associated proteins, and their motor domain interacting with microtubules and associated proteins. Together, these interactions determine the mobility of different endosomal structures. In this Review, we provide a comprehensive overview of the factors regulating the different interactions to tune the fascinating dance of endosomes along microtubules.

ER as master regulator of membrane trafficking and organelle function

The endoplasmic reticulum (ER), which occupies a large portion of the cytoplasm, is the cell’s main site for the biosynthesis of lipids and carbohydrate conjugates, and it is essential for folding, assembly, and biosynthetic transport of secreted proteins and integral membrane proteins. The discovery of abundant membrane contact sites (MCSs) between the ER and other membrane compartments has revealed that, in addition to its biosynthetic and secretory functions, the ER plays key roles in the regulation of organelle dynamics and functions. In this review, we will discuss how the ER regulates endosomes, lysosomes, autophagosomes, mitochondria, peroxisomes, and the Golgi apparatus via MCSs. Such regulation occurs via lipid and Ca2+ transfer and also via control of in trans dephosphorylation reactions and organelle motility, positioning, fusion, and fission. The diverse controls of other organelles via MCSs manifest the ER as master regulator of organelle biology.

Lysosomal positioning diseases: beyond substrate storage

Lysosomal storage diseases (LSDs) comprise a group of inherited monogenic disorders characterized by lysosomal dysfunctions due to undegraded substrate accumulation. They are caused by a deficiency in specific lysosomal hydrolases involved in cellular catabolism, or non-enzymatic proteins essential for normal lysosomal functions. In LSDs, the lack of degradation of the accumulated substrate and its lysosomal storage impairs lysosome functions resulting in the perturbation of cellular homeostasis and, in turn, the damage of multiple organ systems. A substantial number of studies on the pathogenesis of LSDs has highlighted how the accumulation of lysosomal substrates is only the first event of a cascade of processes including the accumulation of secondary metabolites and the impairment of cellular trafficking, cell signalling, autophagic flux, mitochondria functionality and calcium homeostasis, that significantly contribute to the onset and progression of these diseases. Emerging studies on lysosomal biology have described the fundamental roles of these organelles in a variety of physiological functions and pathological conditions beyond their canonical activity in cellular waste clearance. Here, we discuss recent advances in the knowledge of cellular and molecular mechanisms linking lysosomal positioning and trafficking to LSDs.

High-Resolution Low-Power Hyperspectral Line-Scan Imaging of Fast Cellular Dynamics Using Azo-Enhanced Raman Scattering Probes

Small-molecule Raman probes for cellular imaging have attracted great attention owing to their sharp peaks that are sensitive to environmental changes. The small cross section of molecular Raman scattering limits dynamic cellular Raman imaging to expensive and complex coherent approaches that acquire single-channel images and lose hyperspectral Raman information. We introduce a new method, dynamic azo-enhanced Raman imaging (DAERI), to couple the new class of azo-enhanced Raman probes with a high-speed line-scan Raman imaging system. DAERI achieved high-resolution low-power imaging of fast cellular dynamics resolved at ∼270 nm along the confocal direction, 75 μW/μm² and 3.5 s/frame. Based on the azo-enhanced Raman probes with characteristic signals 10²-10⁴ stronger than classic Raman labels, DAERI was not restricted to the cellular Raman-silent region as in prior work and enabled multiplex visualization of organelle motions and interactions. We anticipate DAERI to be a powerful tool for future studies in biophysics and cell biology.

Vesicle choreographies keep up cell-to-extracellular matrix adhesion dynamics in polarized epithelial and endothelial cells

In metazoans, cell adhesion to the extracellular matrix (ECM) drives the development, functioning, and repair of different tissues, organs, and systems. Disruption or dysregulation of cell-to-ECM adhesion promote the initiation and progression of several diseases, such as bleeding, immune disorders and cancer. Integrins are major ECM transmembrane receptors, whose function depends on both allosteric changes and exo-endocytic traffic, which carries them to and from the plasma membrane. In apico-basally polarized cells, asymmetric adhesion to the ECM is maintained by continuous targeting of the plasma membrane by vesicles coming from the trans Golgi network and carrying ECM proteins. Active integrin-bound ECM is indeed endocytosed and replaced by the exocytosis of fresh ECM. Such vesicular traffic is finely driven by the teamwork of microtubules (MTs) and their associated kinesin and dynein motors. Here, we review the main cytoskeletal actors involved in the control of the spatiotemporal distribution of active integrins and their ECM ligands, highlighting the key role of the synchronous (ant)agonistic cooperation between MT motors transporting vesicular cargoes, in the same or in opposite direction, in the regulation of traffic logistics, and the establishment of epithelial and endothelial cell polarity.

Peripubertal requirement of Tsg101 in maintaining the integrity of membranous structures in mouse oocytes

Objective

As a component of Endosomal Sorting Complex Required for Transport (ESCRT) complex I, the tumor susceptibility gene 101 (Tsg101) carries out multiple functions. In this work, we report that oocyte‐specific deletion of tumor susceptibility gene 101 (Tsg101) leads to age‐dependent oocyte demise in mice.

Materials and Method

Tsg101 floxed mice (Tsg101^f/f) were bred with Zp3^cre transgenic mice to examine oocyte‐specific roles of Tsg101. Multiple cellular and molecular biological approaches were taken to examine what leads to oocyte demise in the absence of Tsg101.

Results

The death of oocytes from Zp3^cre/Tsg101^f/f (Tsg101^d/d thereafter) mice showed a strong correlation with sexual maturation, as gonadotropin‐releasing hormone antagonist injections improved the survival rate of oocytes from 5‐week‐old Tsg101^d/d mice. Maturation of oocytes from prepubertal Tsg101^d/d mice proceeded normally, but was largely abnormal in oocytes from peripubertal Tsg101^d/d mice, showing shrinkage or rupture. Endolysosomal structures in oocytes from peripubertal Tsg101^d/d mice showed abnormalities, with aberrant patterns of early and late endosomal markers and a high accumulation of lysosomes. Dying oocytes showed plasma membrane blebs and leakage. Blockage of endocytosis in oocytes at 4°C prevented cytoplasmic shrinkage of oocytes from Tsg101^d/d mice until 9 h. The depletion of tsg‐101 in Caenorhabditis elegans increased the permeability of oocytes and embryos, suggesting a conserved role of Tsg101 in maintaining membrane integrity.

Conclusions

Collectively, Tsg101 plays a dual role in maintaining the integrity of membranous structures, which is influenced by age in mouse oocytes.

Spatial regulation of endosomes in growing dendrites

Many membrane proteins are highly enriched in either dendrites or axons. This non-uniform distribution is a critical feature of neuronal polarity and underlies neuronal function. The molecular mechanisms responsible for polarized distribution of membrane proteins has been studied for some time and many answers have emerged. A less well studied feature of neurons is that organelles are also frequently non-uniformly distributed. For instance, EEA1-positive early endosomes are somatodendritic whereas synaptic vesicles are axonal. In addition, some organelles are present in both axons and dendrites, but not distributed uniformly along the processes. One well known example are lysosomes which are abundant in the soma and proximal dendrite, but sparse in the distal dendrite and the distal axon. The mechanisms that determine the spatial distribution of organelles along dendrites are only starting to be studied. In this review, we will discuss the cell biological mechanisms of how the distribution of diverse sets of endosomes along the proximal-distal axis of dendrites might be regulated. In particular, we will focus on the regulation of bulk homeostatic mechanisms as opposed to local regulation. We posit that immature dendrites regulate organelle motility differently from mature dendrites in order to spatially organize dendrite growth, branching and sculpting.

Dynein Is Required for Rab7-Dependent Endosome Maturation, Retrograde Dendritic Transport, and Degradation

In all cell types, endocytosed cargo is transported along a set of endosomal compartments, which are linked maturationally from early endosomes (EEs) via late endosomes (LEs) to lysosomes. Lysosomes are critical for degradation of proteins that enter through endocytic as well as autophagic pathways. Rab7 is the master regulator of early-to-late endosome maturation, motility, and fusion with lysosomes. We previously showed that most degradative lysosomes are localized in the soma and in the first 25 µm of the dendrite and that bulk degradation of dendritic membrane proteins occurs in/near the soma. Dendritic late endosomes therefore move retrogradely in a Rab7-dependent manner for fusion with somatic lysosomes. We now used cultured E18 rat hippocampal neurons of both sexes to determine which microtubule motor is responsible for degradative flux of late endosomes. Based on multiple approaches (inhibiting dynein/dynactin itself or inhibiting dynein recruitment to endosomes by expressing the C-terminus of the Rab7 effector, RILP), we now demonstrate that net retrograde flux of late endosomes in dendrites is supported by dynein. Inhibition of dynein also delays maturation of somatic endosomes, as evidenced by excessive accumulation of Rab7. In addition, degradation of dendritic cargos is inhibited. Our results also suggest that GDP-GTP cycling of Rab7 appears necessary not only for endosomal maturation but also for fusion with lysosomes subsequent to arrival in the soma. In conclusion, Rab7-dependent dynein/dynactin recruitment to dendritic endosomes plays multifaceted roles in dendritic endosome maturation as well as retrograde transport of late endosomes to sustain normal degradative flux.SIGNIFICANCE STATEMENT Lysosomes are critical for degradation of membrane and extracellular proteins that enter through endocytosis. Lysosomes are also the endpoint of autophagy and thus responsible for protein and organelle homeostasis. Endosomal-lysosomal dysfunction is linked to neurodegeneration and aging. We identify roles in dendrites for two proteins with links to human diseases, Rab7 and dynein. Our previous work identified a process that requires directional retrograde transport in dendrites, namely, efficient degradation of short-lived membrane proteins. Based on multiple approaches, we demonstrate that Rab7-dependent recruitment of dynein motors supports net retrograde transport to lysosomes and is needed for endosome maturation. Our data also suggest that GDP-GTP cycling of Rab7 is required for fusion with lysosomes and degradation, subsequent to arrival in the soma.

Axonal transport of Hrs is activity dependent and facilitates synaptic vesicle protein degradation

This study describes an activity-dependent mechanism for transporting ESCRT-0 protein Hrs to synaptic vesicle (SV) pools, facilitating SV protein degradation in response to increased neuronal firing.

Turnover of synaptic vesicle (SV) proteins is vital for the maintenance of healthy and functional synapses. SV protein turnover is driven by neuronal activity in an endosomal sorting complex required for transport (ESCRT)-dependent manner. Here, we characterize a critical step in this process: axonal transport of ESCRT-0 component Hrs, necessary for sorting proteins into the ESCRT pathway and recruiting downstream ESCRT machinery to catalyze multivesicular body (MVB) formation. We find that neuronal activity stimulates the formation of presynaptic endosomes and MVBs, as well as the motility of Hrs+ vesicles in axons and their delivery to SV pools. Hrs+ vesicles co-transport ESCRT-0 component STAM1 and comprise a subset of Rab5+ vesicles, likely representing pro-degradative early endosomes. Furthermore, we identify kinesin motor protein KIF13A as essential for the activity-dependent transport of Hrs to SV pools and the degradation of SV membrane proteins. Together, these data demonstrate a novel activity- and KIF13A-dependent mechanism for mobilizing axonal transport of ESCRT machinery to facilitate the degradation of SV membrane proteins.

Rab39 and its effector UACA regulate basolateral exosome release from polarized epithelial cells

Exosomes are small extracellular vesicles that originate from the intraluminal vesicles of multivesicular bodies (MVBs). We previously reported that polarized Madin-Darby canine kidney (MDCK) epithelial cells secrete two types of exosomes, apical and basolateral exosomes, from different MVBs. However, how these MVBs are selectively targeted to the apical or basolateral membrane remained unknown. Here, we analyze members of the Rab family small GTPases and show that different sets of Rabs mediate asymmetrical exosome release. Rab27, the best-known regulator of MVB transport for exosome release, is specifically but partially involved in apical exosome release, and Rab37, a close homolog of Rab27, is an additional apical exosome regulator. By contrast, Rab39 functions as a specific regulator of basolateral exosome release. Mechanistically, Rab39 interacts with its effector UACA, and UACA then recruits Lyspersin, a component of BLOC-1-related complex (BORC). Our findings suggest that the Rab39-UACA-BORC complex specifically mediates basolateral exosome release.

Computational-Based Discovery of the Anti-Cancer Activities of Pyrrole-Based Compounds Targeting the Colchicine-Binding Site of Tubulin

Despite the tubulin-binding agents (TBAs) that are widely used in the clinic for cancer therapy, tumor resistance to TBAs (both inherited and acquired) significantly impairs their effectiveness, thereby decreasing overall survival (OS) and progression-free survival (PFS) rates, especially for the patients with metastatic, recurrent, and unresectable forms of the disease. Therefore, the development of novel effective drugs interfering with the microtubules’ dynamic state remains a big challenge in current oncology. We report here about the novel ethyl 2-amino-1-(furan-2-carboxamido)-5-(2-aryl/tert-butyl-2-oxoethylidene)-4-oxo-4,5-dihydro-1H-pyrrole-3-carboxylates (EAPCs) exhibiting potent anti-cancer activities against the breast and lung cancer cell lines in vitro. This was due to their ability to inhibit tubulin polymerization and induce cell cycle arrest in M-phase. As an outcome, the EAPC-treated cancer cells exhibited a significant increase in apoptosis, which was evidenced by the expression of cleaved forms of PARP, caspase-3, and increased numbers of Annexin-V-positive cells. By using the in silico molecular modeling methods (e.g., induced-fit docking, binding metadynamics, and unbiased molecular dynamics), we found that EAPC-67 and -70 preferentially bind to the colchicine-binding site of tubulin. Lastly, we have shown that the EAPCs indicated above and colchicine utilizes a similar molecular mechanism to inhibit tubulin polymerization via targeting the T7 loop in the β-chain of tubulin, thereby preventing the conformational changes in the tubulin dimers required for their polymerization. Collectively, we identified the novel and potent TBAs that bind to the colchicine-binding site and disrupt the microtubule network. As a result of these events, the compounds induced a robust cell cycle arrest in M-phase and exhibited potent pro-apoptotic activities against the epithelial cancer cell lines in vitro.

Computational-Based Discovery of the Anti-Cancer Activities of Pyrrole-Based Compounds Targeting the Colchicine-Binding Site of Tubulin

Despite the tubulin-binding agents (TBAs) that are widely used in the clinic for cancer therapy, tumor resistance to TBAs (both inherited and acquired) significantly impairs their effectiveness, thereby decreasing overall survival (OS) and progression-free survival (PFS) rates, especially for the patients with metastatic, recurrent, and unresectable forms of the disease. Therefore, the development of novel effective drugs interfering with the microtubules' dynamic state remains a big challenge in current oncology. We report here about the novel ethyl 2-amino-1-(furan-2-carboxamido)-5-(2-aryl/tert-butyl-2-oxoethylidene)-4-oxo-4,5-dihydro-1H-pyrrole-3-carboxylates (EAPCs) exhibiting potent anti-cancer activities against the breast and lung cancer cell lines in vitro. This was due to their ability to inhibit tubulin polymerization and induce cell cycle arrest in M-phase. As an outcome, the EAPC-treated cancer cells exhibited a significant increase in apoptosis, which was evidenced by the expression of cleaved forms of PARP, caspase-3, and increased numbers of Annexin-V-positive cells. By using the in silico molecular modeling methods (e.g., induced-fit docking, binding metadynamics, and unbiased molecular dynamics), we found that EAPC-67 and -70 preferentially bind to the colchicine-binding site of tubulin. Lastly, we have shown that the EAPCs indicated above and colchicine utilizes a similar molecular mechanism to inhibit tubulin polymerization via targeting the T7 loop in the β-chain of tubulin, thereby preventing the conformational changes in the tubulin dimers required for their polymerization. Collectively, we identified the novel and potent TBAs that bind to the colchicine-binding site and disrupt the microtubule network. As a result of these events, the compounds induced a robust cell cycle arrest in M-phase and exhibited potent pro-apoptotic activities against the epithelial cancer cell lines in vitro.

STIM and Orai Mediated Regulation of Calcium Signaling in Age-Related Diseases

Tight spatiotemporal regulation of intracellular Ca²⁺ plays a critical role in regulating diverse cellular functions including cell survival, metabolism, and transcription. As a result, eukaryotic cells have developed a wide variety of mechanisms for controlling Ca²⁺ influx and efflux across the plasma membrane as well as Ca²⁺ release and uptake from intracellular stores. The STIM and Orai protein families comprising of STIM1, STIM2, Orai1, Orai2, and Orai3, are evolutionarily highly conserved proteins that are core components of all mammalian Ca²⁺ signaling systems. STIM1 and Orai1 are considered key players in the regulation of Store Operated Calcium Entry (SOCE), where release of Ca²⁺ from intracellular stores such as the Endoplasmic/Sarcoplasmic reticulum (ER/SR) triggers Ca²⁺ influx across the plasma membrane. SOCE, which has been widely characterized in non-excitable cells, plays a central role in Ca²⁺-dependent transcriptional regulation. In addition to their role in Ca²⁺ signaling, STIM1 and Orai1 have been shown to contribute to the regulation of metabolism and mitochondrial function. STIM and Orai proteins are also subject to redox modifications, which influence their activities. Considering their ubiquitous expression, there has been increasing interest in the roles of STIM and Orai proteins in excitable cells such as neurons and myocytes. While controversy remains as to the importance of SOCE in excitable cells, STIM1 and Orai1 are essential for cellular homeostasis and their disruption is linked to various diseases associated with aging such as cardiovascular disease and neurodegeneration. The recent identification of splice variants for most STIM and Orai isoforms while complicating our understanding of their function, may also provide insight into some of the current contradictions on their roles. Therefore, the goal of this review is to describe our current understanding of the molecular regulation of STIM and Orai proteins and their roles in normal physiology and diseases of aging, with a particular focus on heart disease and neurodegeneration.

Correlative Organelle Microscopy: Fluorescence Guided Volume Electron Microscopy of Intracellular Processes

Intracellular processes depend on a strict spatial and temporal organization of proteins and organelles. Therefore, directly linking molecular to nanoscale ultrastructural information is crucial in understanding cellular physiology. Volume or three-dimensional (3D) correlative light and electron microscopy (volume-CLEM) holds unique potential to explore cellular physiology at high-resolution ultrastructural detail across cell volumes. However, the application of volume-CLEM is hampered by limitations in throughput and 3D correlation efficiency. In order to address these limitations, we describe a novel pipeline for volume-CLEM that provides high-precision (<100 nm) registration between 3D fluorescence microscopy (FM) and 3D electron microscopy (EM) datasets with significantly increased throughput. Using multi-modal fiducial nanoparticles that remain fluorescent in epoxy resins and a 3D confocal fluorescence microscope integrated into a Focused Ion Beam Scanning Electron Microscope (FIB.SEM), our approach uses FM to target extremely small volumes of even single organelles for imaging in volume EM and obviates the need for post-correlation of big 3D datasets. We extend our targeted volume-CLEM approach to include live-cell imaging, adding information on the motility of intracellular membranes selected for volume-CLEM. We demonstrate the power of our approach by targeted imaging of rare and transient contact sites between the endoplasmic reticulum (ER) and lysosomes within hours rather than days. Our data suggest that extensive ER-lysosome and mitochondria-lysosome interactions restrict lysosome motility, highlighting the unique capabilities of our integrated CLEM pipeline for linking molecular dynamic data to high-resolution ultrastructural detail in 3D.

USP17 is required for peripheral trafficking of lysosomes

Expression of the deubiquitinase USP17 is induced by multiple stimuli, including cytokines (IL‐4/6), chemokines (IL‐8, SDF1), and growth factors (EGF), and several studies indicate it is required for cell proliferation and migration. However, the mechanisms via which USP17 impacts upon these cellular functions are unclear. Here, we demonstrate that USP17 depletion prevents peripheral lysosome positioning, as well as trafficking of lysosomes to the cell periphery in response to EGF stimulation. Overexpression of USP17 also increases secretion of the lysosomal protease cathepsin D. In addition, USP17 depletion impairs plasma membrane repair in cells treated with the pore‐forming toxin streptolysin O, further indicating that USP17 is required for lysosome trafficking to the plasma membrane. Finally, we demonstrate that USP17 can deubiquitinate p62, and we propose that USP17 can facilitate peripheral lysosome trafficking by opposing the E3 ligase RNF26 to untether lysosomes from the ER and facilitate lysosome peripheral trafficking, lysosome protease secretion, and plasma membrane repair.

Recent Approaches to the Identification of Novel Microtubule-Targeting Agents

Microtubules are key components of the eukaryotic cytoskeleton with essential roles in cell division, intercellular transport, cell morphology, motility, and signal transduction. They are composed of protofilaments of heterodimers of α-tubulin and β-tubulin organized as rigid hollow cylinders that can assemble into large and dynamic intracellular structures. Consistent with their involvement in core cellular processes, affecting microtubule assembly results in cytotoxicity and cell death. For these reasons, microtubules are among the most important targets for the therapeutic treatment of several diseases, including cancer. The vast literature related to microtubule stabilizers and destabilizers has been reviewed extensively in recent years. Here we summarize recent experimental and computational approaches for the identification of novel tubulin modulators and delivery strategies. These include orphan small molecules, PROTACs as well as light-sensitive compounds that can be activated with high spatio-temporal accuracy and that represent promising tools for precision-targeted chemotherapy.

RUFY3 links Arl8b and JIP4-Dynein complex to regulate lysosome size and positioning

The bidirectional movement of lysosomes on microtubule tracks regulates their whole-cell spatial arrangement. Arl8b, a small GTP-binding (G) protein, promotes lysosome anterograde trafficking mediated by kinesin-1. Herein, we report an Arl8b effector, RUFY3, which regulates the retrograde transport of lysosomes. We show that RUFY3 interacts with the JIP4-dynein-dynactin complex and facilitates Arl8b association with the retrograde motor complex. Accordingly, RUFY3 knockdown disrupts the positioning of Arl8b-positive endosomes and reduces Arl8b colocalization with Rab7-marked late endosomal compartments. Moreover, we find that RUFY3 regulates nutrient-dependent lysosome distribution, although autophagosome-lysosome fusion and autophagic cargo degradation are not impaired upon RUFY3 depletion. Interestingly, lysosome size is significantly reduced in RUFY3 depleted cells, which could be rescued by inhibition of the lysosome reformation regulatory factor PIKFYVE. These findings suggest a model in which the perinuclear cloud arrangement of lysosomes regulates both the positioning and size of these proteolytic compartments.