Involvement of Gβγ subunits of Gi protein coupled with S1P receptor on multivesicular endosomes in F-actin formation and cargo sorting into exosomes

A novel function for exosomes in depression

Exosomes are a class of extracellular vesicles that encompass a diverse array of bioactive molecules, including proteins, lipids, mRNA, and microRNA(miRNA). Virtually all cell types release exosomes under both physiological and pathological conditions. In addition to electrical and chemical signals, exosomes are an alternative route of signaling between cells in the brain. In the brain, they are involved in processes such as synaptic plasticity, neuronal stress response, intercellular communication, and neurogenesis. A number of studies have shown that exosomes regulate the occurrence and development of depression by participating in the regulation of hypothalamic-pituitary-adrenal axis, brain-derived neurotrophic factor, immune inflammatory response and other mechanisms, showing that they may become potential biological agents for the diagnosis and treatment of depression. In addition, exosomes have the ability to easily cross the blood-brain barrier, making them ideal drug or molecular delivery tools for the central nervous system. Engineered exosomes have good brain targeting ability, and their research in central nervous system diseases has begun to emerge. However, the molecular pathways involved in the pathogenesis of depression remain unknown, and further studies are needed to fully understand the role of exosomes in the development or improvement of depression. Therefore, in this review, we mainly focus on the diagnostic performance and therapeutic effect of exosomes in depression, and explore the advantages of exosomes as biomarkers and gene delivery vectors for depression.

Resolving the two-body problem: A postulated role for the V0 sector of the V0V1-ATPase in exosome biogenesis and multivesicular body fate

Because the discovery of the multivesicular body (MVB) as the origin of secreted vesicles or exosomes, the question arose and still looms-what distinguishes an MVB destined for fusion with the plasma membrane (EXO-MVB) facilitating exosome release from an MVB involved in transport of content to the lysosome (LYSO-MVB). Do they have independent origins? Hence, the two-body problem. We hypothesize that a key to this conundrum is the membrane spanning V0 sector of the proton pump, V0V1-ATPase. The V0V1-ATPase participates in the acidification of intracellular compartments, although V0 can function separately from V1 and different V0 isoforms are endowed with membrane binding capabilities that allow the V0V1-ATPase to selectively localize to different endocytic compartments including early and late endosomes and lysosomes. We propose that V0, in collaboration with cholesterol and phosphoinositides, plays a central role in the early endosome as a nucleation center to direct the de novo assembly of an EXO-MVB scaffold. The EXO-MVB scaffold may play multiple roles-operating as an assembly platform, participating in membrane fission as well as providing downstream navigational queues necessary for exosome secretion. Thus, V0 may represent an influential nexus, a starting point, in exosome biogenesis.

Flotillins in membrane trafficking and physiopathology

Flotillin 1 and 2 are highly conserved and homologous members of the stomatin, prohibitin, flotillin, HflK/C (SPFH) family. These ubiquitous proteins assemble into hetero-oligomers at the cytoplasmic membrane in sphingolipid-enriched domains. Flotillins play crucial roles in various cellular processes, likely by concentrating sphingosine. They primarily act as scaffolding protein complexes within membrane microdomains (also called lipid rafts) and induce endocytosis and trafficking. Their diverse cargos in the upregulated flotillin-induced trafficking (UFIT) pathway, including tyrosine kinase receptors, adhesion molecules, and neurotransmitter receptors, link them to a wide range of cellular processes and diseases. Consequently, flotillin upregulation has been associated with various pathological conditions such as cancer, metabolic disorders, and neurodegenerative diseases. Flotillins may also be co-opted by pathogens to facilitate their entry and growth within host cells. In this review, we examined recent advancements in elucidating the structure and functions of the flotillin protein complex, including its implications in favoring the generation of sphingosine 1-phosphate, an essential bioactive lipid. We emphasized how the recent cryo-electron microscopy (cryo-EM) structure of a truncated cone-shaped cage composed of 22 copies of flotillin 1 and 2 subunits has enhanced our understanding of the flotillin complex organization within membrane microdomains and its role in membrane remodeling. We also explored how flotillin upregulation can perturb endosomal trafficking and contribute to various pathologies. A comprehensive understanding of flotillin oligomer organization and function is crucial to developing targeted therapies for diseases associated with flotillin overexpression.

Regulation of cellular and systemic sphingolipid homeostasis

One hundred and fifty years ago, Johann Thudichum described sphingolipids as unusual "Sphinx-like" lipids from the brain. Today, we know that thousands of sphingolipid molecules mediate many essential functions in embryonic development and normal physiology. In addition, sphingolipid metabolism and signalling pathways are dysregulated in a wide range of pathologies, and therapeutic agents that target sphingolipids are now used to treat several human diseases. However, our understanding of sphingolipid regulation at cellular and organismal levels and their functions in developmental, physiological and pathological settings is rudimentary. In this Review, we discuss recent advances in sphingolipid pathways in different organelles, how secreted sphingolipid mediators modulate physiology and disease, progress in sphingolipid-targeted therapeutic and diagnostic research, and the trans-cellular sphingolipid metabolic networks between microbiota and mammals. Advances in sphingolipid biology have led to a deeper understanding of mammalian physiology and may lead to progress in the management of many diseases.

Bioactive sphingolipids as emerging targets for signal transduction in cancer development

Sphingolipids, crucial components of cellular membranes, play a vital role in maintaining cellular structure and signaling integrity. Disruptions in sphingolipid metabolism are increasingly implicated in cancer development. Key bioactive sphingolipids, such as ceramides, sphingosine-1-phosphate (S1P), ceramide-1-phosphate (C1P), and glycosphingolipids, profoundly impact tumor biology. They influence the behavior of tumor cells, stromal cells, and immune cells, affecting tumor aggressiveness, angiogenesis, immune modulation, and extracellular matrix remodeling. Furthermore, abnormal expression of sphingolipids and their metabolizing enzymes modulates the secretion of tumor-derived extracellular vesicles (TDEs), which are key players in creating an immunosuppressive tumor microenvironment, remodeling the extracellular matrix, and facilitating oncogenic signaling within in situ tumors and distant pre-metastatic niches (PMNs). Understanding the role of sphingolipids in the biogenesis of tumor-derived extracellular vesicles (TDEs) and their bioactive contents can pave the way for new biomarkers in cancer diagnosis and prognosis, ultimately enhancing comprehensive tumor treatment strategies.

Exosome nanovesicles: biomarkers and new strategies for treatment of human diseases

Exosomes are nanoscale vesicles of cellular origin. One of the main characteristics of exosomes is their ability to carry a wide range of biomolecules from their parental cells, which are important mediators of intercellular communication and play an important role in physiological and pathological processes. Exosomes have the advantages of biocompatibility, low immunogenicity, and wide biodistribution. As researchers' understanding of exosomes has increased, various strategies have been proposed for their use in diagnosing and treating diseases. Here, we provide an overview of the biogenesis and composition of exosomes, describe the relationship between exosomes and disease progression, and focus on the use of exosomes as biomarkers for early screening, disease monitoring, and guiding therapy in refractory diseases such as tumors and neurodegenerative diseases. We also summarize the current applications of exosomes, especially engineered exosomes, for efficient drug delivery, targeted therapies, gene therapies, and immune vaccines. Finally, the current challenges and potential research directions for the clinical application of exosomes are also discussed. In conclusion, exosomes, as an emerging molecule that can be used in the diagnosis and treatment of diseases, combined with multidisciplinary innovative solutions, will play an important role in clinical applications.

High throughput screening of mesenchymal stromal cell morphological response to inflammatory signals for bioreactor-based manufacturing of extracellular vesicles that modulate microglia

Due to their immunomodulatory function, mesenchymal stromal cells (MSCs) are a promising therapeutic with the potential to treat neuroinflammation associated with neurodegenerative diseases. This function is mediated by secreted extracellular vesicles (MSC-EVs). Despite established safety, MSC clinical translation has been unsuccessful due to inconsistent clinical outcomes resulting from functional heterogeneity. Current approaches to mitigate functional heterogeneity include 'priming' MSCs with inflammatory signals to enhance function. However, comprehensive evaluation of priming and its effects on MSC-EV function has not been performed. Furthermore, clinical translation of MSC-EV therapies requires significant manufacturing scale-up, yet few studies have investigated the effects of priming in bioreactors. As MSC morphology has been shown to predict their immunomodulatory function, we screened MSC morphological response to an array of priming signals and evaluated MSC-EV identity and potency in response to priming in flasks and bioreactors. We identified unique priming conditions corresponding to distinct morphologies. These conditions demonstrated a range of MSC-EV preparation quality and lipidome, allowing us to discover a novel MSC-EV manufacturing condition, as well as gain insight into potential mechanisms of MSC-EV microglia modulation. Our novel screening approach and application of priming to MSC-EV bioreactor manufacturing informs refinement of larger-scale manufacturing and enhancement of MSC-EV function.

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

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

Treating cancer through modulating exosomal protein loading and function: The prospects of natural products and traditional Chinese medicine

Exosomes, small yet vital extracellular vesicles, play an integral role in intercellular communication. They transport critical components, such as proteins, lipid bilayers, DNA, RNA, and glycans, to target cells. These vesicles are crucial in modulating the extracellular matrix and orchestrating signal transduction processes. In oncology, exosomes are pivotal in tumor growth, metastasis, drug resistance, and immune modulation within the tumor microenvironment. Exosomal proteins, noted for their stability and specificity, have garnered widespread attention. This review delves into the mechanisms of exosomal protein loading and their impact on tumor development, with a focus on the regulatory effects of natural products and traditional Chinese medicine on exosomal protein loading and function. These insights not only offer new strategies and methodologies for cancer treatment but also provide scientific bases and directions for future clinical applications.

Versatile extracellular vesicle-mediated information transfer: intercellular synchronization of differentiation and of cellular phenotypes, and future perspectives

In recent years, extracellular vesicles (EVs) have attracted significant attention as carriers in intercellular communication. The vast array of information contained within EVs is critical for various cellular activities, such as proliferation and differentiation of multiple cell types. Moreover, EVs are being employed in disease diagnostics, implicated in disease etiology, and have shown promise in tissue repair. Recently, a phenomenon has been discovered in which cellular phenotypes, including the progression of differentiation, are synchronized among cells via EVs. This synchronization could be prevalent in widespread different situations in embryogenesis and tissue organization and maintenance. Given the increasing research on multi-cellular tissues and organoids, the role of EV-mediated intercellular communication has become increasingly crucial. This review begins with fundamental knowledge of EVs and then discusses recent findings, various modes of information transfer via EVs, and synchronization of cellular phenotypes.

The Regulation of Exosome Generation and Function in Physiological and Pathological Processes

Exosomes, a type of extracellular vesicle with a diameter of approximately 100 nm that is secreted by all cells, regulate the phenotype and function of recipient cells by carrying molecules such as proteins, nucleic acids, and lipids and are important mediators of intercellular communication. Exosomes are involved in various physiological and pathological processes such as immunomodulation, angiogenesis, tumorigenesis, metastasis, and chemoresistance. Due to their excellent properties, exosomes have shown their potential application in the clinical diagnosis and treatment of disease. The functions of exosomes depend on their biogenesis, uptake, and composition. Thus, a deeper understanding of these processes and regulatory mechanisms can help to find new targets for disease diagnosis and therapy. Therefore, this review summarizes and integrates the recent advances in the regulatory mechanisms of the entire biological process of exosomes, starting from the formation of early-sorting endosomes (ESCs) by plasma membrane invagination to the release of exosomes by fusion of multivesicular bodies (MVBs) with the plasma membrane, as well as the regulatory process of the interactions between exosomes and recipient cells. We also describe and discuss the regulatory mechanisms of exosome production in tumor cells and the potential of exosomes used in cancer diagnosis and therapy.

High throughput screening of mesenchymal stromal cell morphological response to inflammatory signals for bioreactor-based manufacturing of extracellular vesicles that modulate microglia

Due to their immunomodulatory function, mesenchymal stromal cells (MSCs) are a promising therapeutic with the potential to treat neuroinflammation associated with neurodegenerative diseases. This function can be mediated by secreted extracellular vesicles (MSC-EVs). Despite established safety, MSC clinical translation has been unsuccessful due to inconsistent clinical outcomes resulting from functional heterogeneity. Current approaches to mitigate functional heterogeneity include 'priming' MSCs with inflammatory signals to enhance function. However, comprehensive evaluation of priming and its effects on MSC-EV function has not been performed. Clinical translation of MSC-EV therapies requires significant manufacturing scale-up, yet few studies have investigated the effects of priming in bioreactors. As MSC morphology has been shown to predict their immunomodulatory function, we screened MSC morphological response to an array of priming signals and evaluated MSC-EV identity and potency in response to priming in flasks and bioreactors. We identified unique priming conditions corresponding to distinct morphologies. These conditions demonstrated a range of MSC-EV preparation quality and lipidome, allowing us to discover a novel MSC-EV manufacturing condition, as well as gain insight into potential mechanisms of MSC-EV microglia modulation. Our novel screening approach and application of priming to MSC-EV bioreactor manufacturing informs refinement of larger-scale manufacturing and enhancement of MSC-EV function.

Soluble mutant huntingtin drives early human pathogenesis in Huntington's disease

Huntington's disease (HD) is an incurable inherited brain disorder characterised by massive degeneration of striatal neurons, which correlates with abnormal accumulation of misfolded mutant huntingtin (mHTT) protein. Research on HD has been hampered by the inability to study early dysfunction and progressive degeneration of human striatal neurons in vivo. To investigate human pathogenesis in a physiologically relevant context, we transplanted human pluripotent stem cell-derived neural progenitor cells (hNPCs) from control and HD patients into the striatum of new-born mice. Most hNPCs differentiated into striatal neurons that projected to their target areas and established synaptic connexions within the host basal ganglia circuitry. Remarkably, HD human striatal neurons first developed soluble forms of mHTT, which primarily targeted endoplasmic reticulum, mitochondria and nuclear membrane to cause structural alterations. Furthermore, HD human cells secreted extracellular vesicles containing mHTT monomers and oligomers, which were internalised by non-mutated mouse striatal neurons triggering cell death. We conclude that interaction of mHTT soluble forms with key cellular organelles initially drives disease progression in HD patients and their transmission through exosomes contributes to spread the disease in a non-cell autonomous manner.

Context-specific regulation of extracellular vesicle biogenesis and cargo selection

To coordinate, adapt and respond to biological signals, cells convey specific messages to other cells. An important aspect of cell-cell communication involves secretion of molecules into the extracellular space. How these molecules are selected for secretion has been a fundamental question in the membrane trafficking field for decades. Recently, extracellular vesicles (EVs) have been recognized as key players in intercellular communication, carrying not only membrane proteins and lipids but also RNAs, cytosolic proteins and other signalling molecules to recipient cells. To communicate the right message, it is essential to sort cargoes into EVs in a regulated and context-specific manner. In recent years, a wealth of lipidomic, proteomic and RNA sequencing studies have revealed that EV cargo composition differs depending upon the donor cell type, metabolic cues and disease states. Analyses of distinct cargo 'fingerprints' have uncovered mechanistic linkages between the activation of specific molecular pathways and cargo sorting. In addition, cell biology studies are beginning to reveal novel biogenesis mechanisms regulated by cellular context. Here, we review context-specific mechanisms of EV biogenesis and cargo sorting, focusing on how cell signalling and cell state influence which cellular components are ultimately targeted to EVs.

Epsin1-mediated exosomal sorting of Dll4 modulates the tubular-macrophage crosstalk in diabetic nephropathy

Tubular epithelial cells (TECs) play critical roles in the development of diabetic nephropathy (DN), and can activate macrophages through the secretion of exosomes. However, the mechanism(s) of TEC-exosomes in macrophage activation under DN remains unknown. By mass spectrometry, 1,644 differentially expressed proteins, especially Dll4, were detected in the urine exosomes of DN patients compared with controls, which was confirmed by western blot assay. Elevated Epsin1 and Dll4/N1ICD expression was observed in kidney tissues in both DN patients and db/db mice and was positively associated with tubulointerstitial damage. Exosomes from high glucose (HG)-treated tubular cells (HK-2) with Epsin1 knockdown (KD) ameliorated macrophage activation, TNF-α, and IL-6 expression, and tubulointerstitial damage in C57BL/6 mice in vivo. In an in vitro study, enriched Dll4 was confirmed in HK-2 cells stimulated with HG, which was captured by THP-1 cells and promoted M1 macrophage activation. In addition, Epsin1 modulated the content of Dll4 in TEC-exosomes stimulated with HG. TEC-exosomes with Epsin1-KD significantly inhibited N1ICD activation and iNOS expression in THP-1 cells compared with incubation with HG alone. These findings suggested that Epsin1 could modulate tubular-macrophage crosstalk in DN by mediating exosomal sorting of Dll4 and Notch1 activation.

Protein corona and exosomes: new challenges and prospects

Recent advances in extracellular vesicle (EVs) detection and isolation methods have led to the development of novel therapeutic modalities. Among different types of EVs, exosomes (Exos) can transfer different signaling biomolecules and exhibit several superior features compared to whole-cell-based therapies. Therapeutic factors are normally loaded into the Exo lumen or attached to their surface for improving the on-target delivery rate and regenerative outcomes. Despite these advantages, there are several limitations in the application of Exos in in vivo conditions. It was suggested that a set of proteins and other biological compounds are adsorbed around Exos in aqueous phases and constitute an external layer named protein corona (PC). Studies have shown that PC can affect the physicochemical properties of synthetic and natural nanoparticles (NPs) after introduction in biofluids. Likewise, PC is generated around EVs, especially Exos in in vivo conditions. This review article is a preliminary attempt to address the interfering effects of PC on Exo bioactivity and therapeutic effects. Video Abstract.

Non-canonical Golgi-compartmentalized Gβγ signaling: mechanisms, functions, and therapeutic targets

G protein Gβγ subunits are key mediators of G protein-coupled receptor (GPCR) signaling under physiological and pathological conditions; their inhibitors have been tested for the treatment of human disease. Conventional wisdom is that the Gβγ complex is activated and subsequently exerts its functions at the plasma membrane (PM). Recent studies have revealed non-canonical activation of Gβγ at intracellular organelles, where the Golgi apparatus is a major locale, via translocation or local activation. Golgi-localized Gβγ activates specific signaling cascades and regulates fundamental cell processes such as membrane trafficking, proliferation, and migration. More recent studies have shown that inhibiting Golgi-compartmentalized Gβγ signaling attenuates cardiomyocyte hypertrophy and prostate tumorigenesis, indicating new therapeutic targets. We review novel activation mechanisms and non-canonical functions of Gβγ at the Golgi, and discuss potential therapeutic interventions by targeting Golgi-biased Gβγ-directed signaling.

Exosome biogenesis: machinery, regulation, and therapeutic implications in cancer

Exosomes are well-known key mediators of intercellular communication and contribute to various physiological and pathological processes. Their biogenesis involves four key steps, including cargo sorting, MVB formation and maturation, transport of MVBs, and MVB fusion with the plasma membrane. Each process is modulated through the competition or coordination of multiple mechanisms, whereby diverse repertoires of molecular cargos are sorted into distinct subpopulations of exosomes, resulting in the high heterogeneity of exosomes. Intriguingly, cancer cells exploit various strategies, such as aberrant gene expression, posttranslational modifications, and altered signaling pathways, to regulate the biogenesis, composition, and eventually functions of exosomes to promote cancer progression. Therefore, exosome biogenesis-targeted therapy is being actively explored. In this review, we systematically summarize recent progress in understanding the machinery of exosome biogenesis and how it is regulated in the context of cancer. In particular, we highlight pharmacological targeting of exosome biogenesis as a promising cancer therapeutic strategy.

Filamin FLN-2 promotes MVB biogenesis by mediating vesicle docking on the actin cytoskeleton

Multivesicular bodies (MVBs) contain intralumenal vesicles that are delivered to lysosomes for degradation or released extracellularly for intercellular signaling. Here, we identified Caenorhabditis elegans filamin FLN-2 as a novel regulator of MVB biogenesis. FLN-2 co-localizes with V-ATPase subunits on MVBs, and the loss of FLN-2 affects MVB biogenesis, reducing the number of MVBs in C. elegans hypodermis. FLN-2 associates with actin filaments and is required for F-actin organization. Like fln-2(lf) mutation, inactivation of the V0 or V1 sector of V-ATPase or inhibition of actin polymerization impairs MVB biogenesis. Super-resolution imaging shows that FLN-2 docks V-ATPase-decorated MVBs onto actin filaments. FLN-2 interacts via its calponin-homology domains with F-actin and the V1-E subunit, VHA-8. Our data suggest that FLN-2 mediates the docking of MVBs on the actin cytoskeleton, which is required for MVB biogenesis.

Agonist-induced extracellular vesicles contribute to the transfer of functional bombesin receptor-subtype 3 to recipient cells

Extracellular vesicles (EVs) are important carriers for biomolecules in the microenvironment that greatly promote intercellular and extracellular communications. However, it is unclear whether bombesin receptor-subtype 3 (BRS-3), an orphan G-protein coupled receptor, can be packed into EVs and functionally transferred to recipient cells. In this study, we applied the synthetic agonist and antagonist to activate and inhibit the BRS-3 in HEK293-BRS-3 cells, whose EVs release was BRS-3 activation dependent. The presence of BRS-3 in harvested EVs was further confirmed by an enhanced green fluorescent protein tag. After recipient cells were co-cultured with these EVs, the presence of BRS-3 in the recipient cells was discovered, whose function was experimentally validated. Quantitative proteomics approach was utilized to decipher the proteome of the EVs derived from HEK293-BRS-3 cells after different stimulations. More than 900 proteins were identified, including 51 systematically dysregulated EVs proteins. The Ingenuity Pathway Analysis (IPA) revealed that RhoA signaling pathway was as an essential player for the secretion of EVs. Selective inhibition of RhoA signaling pathway after BRS-3 activation dramatically reversed the increased secretion of EVs. Our data, collectively, demonstrated that EVs contributed to the transfer of functional BRS-3 to the recipient cells, whose secretion was partially regulated by RhoA signaling pathway.

Exosomes: Breast cancer-derived extracellular vesicles; recent key findings and technologies in disease progression, diagnostics, and cancer targeting

Breast cancer is one of the most frequently diagnosed types of cancer in women. Metastasis, particularly to the lungs and brain, increases mortality in breast cancer patients. Recently, breast cancer-related exosomes have received significant attention because of their key role in breast cancer progression. As a result, numerous exosome-based therapeutic tools for diagnosis and treatment have been developed, and their biological and chemical mechanisms have been explored. This review summarizes up-to-date advanced key findings and technologies in breast cancer progression, diagnostics, and targeting. We focused on recent research on the basic biology of exosomes and disease-related exosomal genes and proteins, as well as their signal transduction in cell-to-cell communications, diagnostic markers, and exosome-based antibreast cancer technologies. We also paid special attention to technologies employing exosomes modified with functional peptides for the targeted delivery of therapeutic and diagnostic agents.

Constitutive activation of S1P receptors at the trans-Golgi network is required for surface transport carrier formation

The importance of the G-protein βγ subunits in the regulation of cargo transport from the trans-Golgi network (TGN) to the plasma membrane (PM) is well accepted; however, the molecular mechanism underlying the G-protein activation at the TGN remains unclear. We show here that sphingosine 1-phosphate (S1P) receptors at the PM were trafficked to the TGN in response to a surface transport cargo, temperature-sensitive vesicular stomatitis virus glycoprotein tagged with green fluorescent protein accumulation in the Golgi. The receptor internalization occurred in an S1P-independent manner but required phosphorylation by G-protein receptor kinase 2 and β-arrestin association before internalization. Continuously activated S1P receptors in a manner dependent on S1P at the TGN kept transmitting G-protein signals including the βγ subunits supply necessary for transport carrier formation at the TGN destined for the PM.

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S1P receptors traffic from the PM to Golgi in a surface cargo-dependent manner

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S1PR trafficking follows GRK2-dependent phosphorylation and β-arrestin binding

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S1PRs at the Golgi are continuously activated by S1P while sending G-protein signals

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S1PR/Gβγ signals at the Golgi are indispensable for surface transport carrier formation

Novel functions of S1P in chronic itchy and inflammatory skin diseases

S1P is a pleotropic sphingolipid signalling molecule that acts through binding to five high-affinity G-protein coupled receptors. S1P-signaling affects cell fate in a multitude of ways, e.g. influencing cell differentiation, proliferation, and apoptosis, as well as playing an important role in immune cell trafficking. Though many effects of S1P-signaling in the human body have been discovered, the full range of functions is yet to be understood. For inflammatory skin diseases such as atopic dermatitis and psoriasis, evidence is emerging that dysfunction and imbalance of the S1P-axis is a contributing factor. Multiple studies investigating the efficacy of S1PR modulators in alleviating the severity and symptoms of skin conditions in various animal models and human clinical trials have shown promising results and validated the interest in the S1P-axis as a potential therapeutic target. Even though the involvement of S1P-signalling in inflammatory skin diseases still requires further clarification, the implications of the recent findings may prompt expansion of research to additional skin conditions and more S1P-axis modulatory pharmaceuticals.

Ubiquitination-Dependent Regulation of Small GTPases in Membrane Trafficking: From Cell Biology to Human Diseases

Membrane trafficking is critical for cellular homeostasis, which is mainly carried out by small GTPases, a class of proteins functioning in vesicle budding, transport, tethering and fusion processes. The accurate and organized membrane trafficking relies on the proper regulation of small GTPases, which involves the conversion between GTP- and GDP-bound small GTPases mediated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Emerging evidence indicates that post-translational modifications (PTMs) of small GTPases, especially ubiquitination, play an important role in the spatio-temporal regulation of small GTPases, and the dysregulation of small GTPase ubiquitination can result in multiple human diseases. In this review, we introduce small GTPases-mediated membrane trafficking pathways and the biological processes of ubiquitination-dependent regulation of small GTPases, including the regulation of small GTPase stability, activity and localization. We then discuss the dysregulation of small GTPase ubiquitination and the associated human membrane trafficking-related diseases, focusing on the neurological diseases and infections. An in-depth understanding of the molecular mechanisms by which ubiquitination regulates small GTPases can provide novel insights into the membrane trafficking process, which knowledge is valuable for the development of more effective and specific therapeutics for membrane trafficking-related human diseases.

Non-coding RNAs and lipids mediate the function of extracellular vesicles in cancer cross-talk

Research on extracellular vesicles (EVs) has been expanded, especially in the field of cancer. The cargoes in EVs, especially those in small EVs such as exosomes include microRNAs (miRNAs), mRNA, proteins, and lipids, are assumed to work cooperatively in the tumor microenvironment. In 2007, it was reported that miRNAs were abundant among the non-coding RNAs present in exosomes. Since then, many studies have investigated the functions of miRNAs and have tried to apply these molecules to aid in the diagnosis of cancer. Accordingly, many reviews of non-coding RNAs in EVs have been published for miRNAs. This review focuses on relatively new cargoes, covering long noncoding (lnc) RNAs, circular RNAs, and repeat RNAs, among non-coding RNAs. These RNAs, regardless of EV or cell type, have newly emerged due to the innovation of sequencing technology. The poor conservation, low quantity, and technical difficulty in detecting these RNA types have made it difficult to elucidate their functions and expression patterns. We herein summarize a limited number of studies. Although lipids are major components of EVs, current research on EVs focuses on miRNA and protein biology, while the roles of lipids in exosomes have not drawn attention. However, several recent studies revealed that phospholipids, which are components of the EV membrane, play important roles in the intercommunication between cells and in the generation of lipid mediators. Here, we review the reported roles of these molecules, and describe their potential in cancer biology.

Biofunctional Peptide-Modified Extracellular Vesicles Enable Effective Intracellular Delivery via the Induction of Macropinocytosis

We previously reported that macropinocytosis (accompanied by actin reorganization, ruffling of the plasma membrane, and engulfment of large volumes of extracellular fluid) is an important process for the cellular uptake of extracellular vesicles, exosomes. Accordingly, we developed techniques to induce macropinocytosis by the modification of biofunctional peptides on exosomal membranes, thereby enhancing their cellular uptake. Arginine-rich cell-penetrating peptides have been shown to induce macropinocytosis via proteoglycans; accordingly, we developed peptide-modified exosomes that could actively induce macropinocytotic uptake by cells. In addition, the activation of EGFR induces macropinocytosis; based on this knowledge, we developed artificial leucine-zipper peptide (K4)-modified exosomes. These exosomes can recognize E3 sequence-fused EGFR (E3-EGFR), leading to the clustering and activation of E3-EGFR by coiled-coil formation (E3/K4), which induces cellular exosome uptake by macropinocytosis. In addition, modification of pH-sensitive fusogenic peptides (e.g., GALA) also enhances the cytosolic release of exosomal contents. These experimental techniques and findings using biofunctional peptides have contributed to the development of exosome-based intracellular delivery systems.

Involvement of Receptor-Mediated S1P Signaling in EGF-Induced Macropinocytosis in COS7 Cells

Macropinocytosis is a highly conserved cellular process of endocytosis by which extracellular fluid and nutrients are taken up into cells through large, heterogeneous vesicles known as macropinosomes. Growth factors such as epidermal growth factor (EGF) can induce macropinocytosis in many types of cells, although precise mechanism underlying EGF-induced macropinocytosis remains unclear. In the present studies we have shown the involvement of S1P signaling in EGF-induced macropinocytosis in COS7 cells. First, EGF-induced macropinocytosis was strongly impaired in sphingosine kinase isozymes, SphK1 or SphK2-depleted cells, which was completely rescued by the expression of the corresponding wild-type isozyme but not the catalytically inactive one, suggesting the involvement of sphingosine 1-phosphate (S1P) in this phenomenon. Next, we observed that EGF-induced macropinocytosis was strongly inhibited in S1P type 1 receptor (S1P1R)-knockdown cells, implying involvement of S1P1R in this event. Furthermore, we could successfully demonstrate EGF-induced trans-activation of S1P1R using one-molecular fluorescence resonance energy transfer (FRET) technique. Moreover, for EGF-induced Rac1 activation, a step essential to F-actin formation and subsequent macropinocytosis, S1P signaling is required for its full activation, as judged by FRET analysis. These findings indicate that growth factors such as EGF utilize receptor-mediated S1P signaling for the regulation of macropinocytosis to fulfil vital cell activity.

The role of exosome lipids in central nervous system diseases

Central nervous system (CNS) diseases are common diseases that threaten human health. The CNS is highly enriched in lipids, which play important roles in maintaining normal physiological functions of the nervous system. Moreover, many CNS diseases are closely associated with abnormal lipid metabolism. Exosomes are a subtype of extracellular vesicles (EVs) secreted from multivesicular bodies (MVBs) . Through novel forms of intercellular communication, exosomes secreted by brain cells can mediate inter-neuronal signaling and play important roles in the pathogenesis of CNS diseases. Lipids are essential components of exosomes, with cholesterol and sphingolipid as representative constituents of its bilayer membrane. In the CNS, lipids are closely related to the formation and function of exosomes. Their dysregulation causes abnormalities in exosomes, which may, in turn, lead to dysfunctions in inter-neuronal communication and promote diseases. Therefore, the role of lipids in the treatment of neurological diseases through exosomes has received increasing attention. The aim of this review is to discuss the relationship between lipids and exosomes and their roles in CNS diseases.

New Insights into the Role of Sphingolipid Metabolism in Melanoma

Cutaneous melanoma is a deadly skin cancer whose aggressiveness is directly linked to its metastatic potency. Despite remarkable breakthroughs in term of treatments with the emergence of targeted therapy and immunotherapy, the prognosis for metastatic patients remains uncertain mainly because of resistances. Better understanding the mechanisms responsible for melanoma progression is therefore essential to uncover new therapeutic targets. Interestingly, the sphingolipid metabolism is dysregulated in melanoma and is associated with melanoma progression and resistance to treatment. This review summarises the impact of the sphingolipid metabolism on melanoma from the initiation to metastatic dissemination with emphasis on melanoma plasticity, immune responses and resistance to treatments.

The Convergence of Extracellular Vesicle and GPCR Biology

Transmembrane receptors, of which G protein-coupled receptors (GPCRs) constitute the largest group, typically act as cellular antennae that reside at the plasma membrane (PM) to collect and interpret information from the extracellular environment. The discovery of cell-released extracellular vesicles (EVs) has added a new dimension to intercellular communication. These unique nanocarriers reflect cellular topology and can systemically transport functionally competent transmembrane receptors, ligands, and a cargo of signal proteins. Recent developments hint at roles for GPCRs in the EV life cycle and, conversely, at roles for EVs in GPCR signal transduction. We highlight key points of convergence, discuss their relevance to current GPCR and EV paradigms, and speculate on how this intersection could lend itself to future therapeutic avenues.

Comprehensive landscape of extracellular vesicle-derived RNAs in cancer initiation, progression, metastasis and cancer immunology

Extracellular vesicles (EVs), a class of heterogeneous membrane vesicles, are generally divided into exosomes and microvesicles on basis of their origination from the endosomal membrane or the plasma membrane, respectively. EV-mediated bidirectional communication among various cell types supports cancer cell growth and metastasis. EVs derived from different cell types and status have been shown to have distinct RNA profiles, comprising messenger RNAs and non-coding RNAs (ncRNAs). Recently, ncRNAs have attracted great interests in the field of EV-RNA research, and growing numbers of ncRNAs ranging from microRNAs to long ncRNAs have been investigated to reveal their specific functions and underlying mechanisms in the tumor microenvironment and premetastatic niches. Emerging evidence has indicated that EV-RNAs are essential functional cargoes in modulating hallmarks of cancers and in reciprocal crosstalk within tumor cells and between tumor and stromal cells over short and long distance, thereby regulating the initiation, development and progression of cancers. In this review, we discuss current findings regarding EV biogenesis, release and interaction with target cells as well as EV-RNA sorting, and highlight biological roles and molecular mechanisms of EV-ncRNAs in cancer biology.

Brain Derived Exosomes Are a Double-Edged Sword in Alzheimer's Disease

Brain derived exosomes (BDEs) are extracellular nanovesicles that are collectively released by all cell lineages of the central nervous system and contain cargo from their original cells. They are emerging as key mediators of communication and waste management among neurons, glial cells and connective tissue during both physiological and pathological conditions in the brain. We review the rapidly growing frontier of BDEs biology in recent years including the involvement of exosomes in neuronal development, maintenance and communication through their multiple signaling functions. Particularly, we highlight the important role of exosomes in Alzheimer's disease (AD), both as a pathogenic agent and as a disease biomarker. Our understanding of such unique nanovesicles may offer not only answers about the (patho) physiological course in AD and associated neurodegenerative diseases but also ideal methods to develop these vesicles as vehicles for drug delivery or as tools to monitor brain diseases in a non-invasive manner because crossing the blood brain barrier is an inherent capability of exosomes. BDEs have potential as biomarkers and as therapeutic tools for AD and related brain disorders in the near future.

Reciprocal Regulation of Chaperone-Mediated Autophagy/Microautophagy and Exosome Release

Autophagy-lysosome proteolysis is involved in protein quality control and classified into macroautophagy (MA), microautophagy (mA) and chaperone-mediated autophagy (CMA), by the routes of substrate delivery to lysosomes. Both autophagy-lysosome proteolysis and exosome release are strongly associated with membrane trafficking. In the present study, we investigated how chemical and small interfering RNA (siRNA)-mediated activation and inhibition of these autophagic pathways affect exosome release in AD293 cells. Activation of MA and mA by rapamycin and activation of CMA by mycophenolic acid significantly decreased exosome release. Although lysosomal inhibitors, NH₄Cl and bafilomycin A1, significantly increased exosome release, a MA inhibitor, 3-methyladenine, did not affect. Exosome release was significantly increased by the siRNA-mediated knockdown of LAMP2A, which is crucial for CMA. Inversely, activity of CMA/mA was significantly increased by the prevention of exosome release, which was induced by siRNA-mediated knockdown of Rab27a. These findings indicate that CMA/mA and exosome release are reciprocally regulated. This regulation would be the molecular basis of extracellular release and propagation of misfolded proteins in various neurodegenerative diseases.

An emerging focus on lipids in extracellular vesicles

Extracellular vesicles contain a lipid bilayer membrane that protects the encapsulated material, such as proteins, nucleic acids, lipids and metabolites, from the extracellular environment. These vesicles are released from cells via different mechanisms. During recent years extracellular vesicles have been studied as possible biomarkers for different diseases, as biological nanoparticles for drug delivery, and in basic studies as a tool to understand the structure of biological membranes and the mechanisms involved in vesicular trafficking. Lipids are essential molecular components of extracellular vesicles, but at the moment our knowledge about the lipid composition and the function of lipids in these vesicles is limited. However, the interest of the research community in these molecules is increasing as their role in extracellular vesicles is starting to be acknowledged. In this review, we will present the status of the field and describe what is needed to bring it forward.

Actin and Actin-Associated Proteins in Extracellular Vesicles Shed by Osteoclasts

Extracellular vesicles (EVs) are shed by all eukaryotic cells and have emerged as important intercellular regulators. EVs released by osteoclasts were recently identified as important coupling factors in bone remodeling. They are shed as osteoclasts resorb bone and stimulate osteoblasts to form bone to replace the bone resorbed. We reported the proteomic content of osteoclast EVs with data from two-dimensional, high resolution liquid chromatography/mass spectrometry. In this article, we examine in detail the actin and actin-associated proteins found in osteoclast EVs. Like EVs from other cell types, actin and various actin-associated proteins were abundant. These include components of the polymerization machinery, myosin mechanoenzymes, proteins that stabilize or depolymerize microfilaments, and actin-associated proteins that are involved in regulating integrins. The selective incorporation of actin-associated proteins into osteoclast EVs suggests that they have roles in the formation of EVs and/or the regulatory signaling functions of the EVs. Regulating integrins so that they bind extracellular matrix tightly, in order to attach EVs to the extracellular matrix at specific locations in organs and tissues, is one potential active role for actin-associated proteins in EVs.

MiR-21 in Substance P-induced exosomes promotes cell proliferation and migration in human colonic epithelial cells

Exosomes are cellular vesicles involved in intercellular communication via their specialized molecular cargo, such as miRNAs. Substance P (SP), a neuropeptide/hormone, and its high-affinity receptor, NK-1R, are highly expressed during colonic inflammation. Our previous studies show that SP/NK-1R signaling stimulates differential miRNA expression and promotes colonic epithelial cell proliferation. In this study, we examined whether SP/NK-1R signaling regulates exosome biogenesis and exosome-miRNA cargo sorting. Moreover, we examined the role of SP/NK-1R signaling in exosome-regulated cell proliferation and migration. Exosomes produced by human colonic NCM460 epithelial cells overexpressing NK-1R (NCM460-NK1R) were isolated from culture media. Exosome abundance and uptake were assessed by Western blot analysis (abundance) and Exo-Green fluorescence microscopy (abundance and uptake). Cargo-miRNA levels were assessed by RT-PCR. Cell proliferation and migration were assessed using xCELLigence technology. Colonic epithelial exosomes were isolated from mice pretreated with SP for 3 days. Cell proliferation in vivo was assessed by Ki-67 staining. SP/NK-1R signaling in human colonic epithelial cells (in vitro) and mouse colons (in vivo) increased 1) exosome production, 2) the level of fluorescence in NCM460s treated with Exo-Green-labeled exosomes, and 3) the level of miR-21 in exosome cargo. Moreover, our results showed that SP/NK-1R-induced cell proliferation and migration are at least in part dependent on intercellular communication via exosomal miR-21 in vitro and in vivo. Our results demonstrate that SP/NK-1R signaling regulates exosome biogenesis and induces its miR-21 cargo sorting. Moreover, exosomal miR-21 promotes proliferation and migration of target cells.NEW & NOTEWORTHY Substance P signaling regulates exosome production in human colonic epithelial cells and colonic crypts in wild-type mice. MiR-21 is selectively sorted into exosomes induced by Substance P stimulation and promotes cell proliferation and migration in human colonocytes and mouse colonic crypts.

Plant sphingolipids promote extracellular vesicle release and alleviate amyloid-β pathologies in a mouse model of Alzheimer's disease

The accumulation of amyloid-β protein (Aβ) in brain is linked to the early pathogenesis of Alzheimer’s disease (AD). We previously reported that neuron-derived exosomes promote Aβ clearance in the brains of amyloid precursor protein transgenic mice and that exosome production is modulated by ceramide metabolism. Here, we demonstrate that plant ceramides derived from Amorphophallus konjac, as well as animal-derived ceramides, enhanced production of extracellular vesicles (EVs) in neuronal cultures. Oral administration of plant glucosylceramide (GlcCer) to APP overexpressing mice markedly reduced Aβ levels and plaque burdens and improved cognition in a Y-maze learning task. Moreover, there were substantial increases in the neuronal marker NCAM-1, L1CAM, and Aβ in EVs isolated from serum and brain tissues of the GlcCer-treated AD model mice. Our data showing that plant ceramides prevent Aβ accumulation by promoting EVs-dependent Aβ clearance in vitro and in vivo provide evidence for a protective role of plant ceramides in AD. Plant ceramides might thus be used as functional food materials to ameliorate AD pathology.

Contribution of Extracellular Vesicles in Rebuilding Injured Muscles

Skeletal myofibers are injured due to mechanical stresses experienced during physical activity, or due to myofiber fragility caused by genetic diseases. The injured myofiber needs to be repaired or regenerated to restore the loss in muscle tissue function. Myofiber repair and regeneration requires coordinated action of various intercellular signaling factors-including proteins, inflammatory cytokines, miRNAs, and membrane lipids. It is increasingly being recognized release and transmission of these signaling factors involves extracellular vesicle (EV) released by myofibers and other cells in the injured muscle. Intercellular signaling by these EVs alters the phenotype of their target cells either by directly delivering the functional proteins and lipids or by modifying longer-term gene expression. These changes in the target cells activate downstream pathways involved in tissue homeostasis and repair. The EVs are heterogeneous with regards to their size, composition, cargo, location, as well as time-course of genesis and release. These differences impact on the subsequent repair and regeneration of injured skeletal muscles. This review focuses on how intracellular vesicle production, cargo packaging, and secretion by injured muscle, modulates specific reparative, and regenerative processes. Insights into the formation of these vesicles and their signaling properties offer new understandings of the orchestrated response necessary for optimal muscle repair and regeneration.

Multifaceted Rho GTPase Signaling at the Endomembranes

The Rho family of small GTPases orchestrates fundamental biological processes such as cell cycle progression, cell migration, and actin cytoskeleton dynamics, and their aberrant signaling is linked to numerous human diseases and disorders. Traditionally, active Rho GTPase proteins were proposed to reside and function predominantly at the plasma membrane. While this view still holds true, it is emerging that active pool of multiple Rho GTPases are in part localized to endomembranes such as endosomes and the Golgi. In this review, we will focus on the intracellular pools and discuss how their local activation contributes to the shaping of various cellular processes. Our main focus will be on Rho signaling from the endosomes, Golgi, mitochondria and nucleus and how they regulate multiple cellular events such as receptor trafficking, cell proliferation and differentiation, cell migration and polarity.

Exosomal Induction of Tumor Innervation

The naïve view of tumors as isolated islands of rogue cells has given way to a deeper understanding of cancer as being closer to a foreign organ. This "organ" contains immunologic, vascular, and neural connections to its host that provide not only mechanisms for disease progression but also opportunities for therapeutic intervention. The presence of nerves within tumor tissues has long been appreciated. However, a mechanistic understanding of how tumors recruit nerves has been slower to emerge. Tumor release of neurotrophic factors and axonal guidance molecules likely directs axons toward the tumor bed. Newly emerging data support a contribution of tumor-released exosomes in the induction of axonogenesis toward the tumor. Exosomes, small membrane-bound vesicles that carry a complex cargo (DNA, RNA, miRNA, lipids, and proteins), protect their cargo from the low pH of the tumor microenvironment. They also represent an efficient means of local and distal communication between the tumor and potentially innervating nerves. Likely, a combination of neurotrophins, guidance molecules, and exosomes work in concert to promote tumor innervation. As such, defining the critical components driving tumor innervation will identify new targets for intervention. Moreover, with a deepening understanding, tumor innervation may emerge as a new hallmark of cancer.

Ras and exosome signaling

Ras gene (HRAS, NRAS, and KRAS) has been observed to be mutated and hyper-activated in a significant proportion of cancers. However, mutant Ras remains a challenging therapeutic target. Similarly, inhibition of targets upstream and downstream of Ras has shown limited clinical utility. There have been attempts to develop and deliver mutant K-Ras silencing RNAs either through their encapsulation in liposomes or nanoparticles. However, these approaches show very limited success due to the lack of stability of such carrier molecules alongside associated toxicity. There is a pressing need for the identification of better therapeutic targets for Ras or its associated pathways as well as improvements in the design of superior RNAi delivery systems to suppress mutant K-Ras. More than a decade ago, it was shown that aggregates of palmitoylated Ras isoforms (H-Ras and N-Ras) passage through the cytosol on rapidly moving nanosized particles ("rasosomes"). Fast forward a decade, considerable new knowledge has emerged in the area of small vesicles, microparticles, and exosomes. Exosomes are tiny vesicles and play a significant role in regulating cancer-related signaling pathways. Exosomes have also been studied as delivery vehicles to transport drugs, proteins, and microRNAs of choice for therapeutic purposes. K-Ras pathway proteins have been implicated in exosome biogenesis and extravasation processes. This review provides an update on the current knowledge related to K-Ras signaling and exosomes and also discusses how these tiny vesicles can be harnessed to successfully deliver the K-Ras silencing moieties.

The Role of Ceramide and Sphingosine-1-Phosphate in Alzheimer's Disease and Other Neurodegenerative Disorders

Bioactive sphingolipids-ceramide, sphingosine, and their respective 1-phosphates (C1P and S1P)-are signaling molecules serving as intracellular second messengers. Moreover, S1P acts through G protein-coupled receptors in the plasma membrane. Accumulating evidence points to sphingolipids' engagement in brain aging and in neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis. Metabolic alterations observed in the course of neurodegeneration favor ceramide-dependent pro-apoptotic signaling, while the levels of the neuroprotective S1P are reduced. These trends are observed early in the diseases' development, suggesting causal relationship. Mechanistic evidence has shown links between altered ceramide/S1P rheostat and the production, secretion, and aggregation of amyloid β/α-synuclein as well as signaling pathways of critical importance for the pathomechanism of protein conformation diseases. Sphingolipids influence multiple aspects of Akt/protein kinase B signaling, a pathway that regulates metabolism, stress response, and Bcl-2 family proteins. The cross-talk between sphingolipids and transcription factors including NF-κB, FOXOs, and AP-1 may be also important for immune regulation and cell survival/death. Sphingolipids regulate exosomes and other secretion mechanisms that can contribute to either the spread of neurotoxic proteins between brain cells, or their clearance. Recent discoveries also suggest the importance of intracellular and exosomal pools of small regulatory RNAs in the creation of disturbed signaling environment in the diseased brain. The identified interactions of bioactive sphingolipids urge for their evaluation as potential therapeutic targets. Moreover, the early disturbances in sphingolipid metabolism may deliver easily accessible biomarkers of neurodegenerative disorders.

Quantitative Analysis of Cargo Density in Single-extracellular Vesicles by Imaging

Function of extracellular vesicles such as exosomes and microvesicles is determined by their wide ranges of cargoes inside them. Even in the pure exosomes or microvesicles the cargo contents are very heterogeneous. To understand this heterogeneous nature of extracellular vesicles, we need information of the vesicles, which will give us some parameters including vesicle size, number and cargo content of each vesicle. Here, we describe a new method to quantify cargo density in single-extracellular vesicles. Staining of extracellular vesicles in a membrane lipid content-proportionate manner and immobilization of extracellular vesicles onto glass substrate allow us to obtain cargo density information of single-extracellular vesicles. This protocol will be useful to analyze the effects of various drugs or genetic manipulation on vesicle generation and maturation including cargo sorting into heterogeneous extracellular vesicles.

Molecular mechanisms of biogenesis of apoptotic exosome-like vesicles and their roles as damage-associated molecular patterns

Recent research has led to contradictory notions regarding the conventional theory that apoptotic cell death can evoke inflammatory or immunogenic responses orchestrated by released damage-associated patterns (DAMPs). By inducing IL-1β from bone marrow-derived macrophages in an effort to determine the inflammatory mediators released from apoptotic cells, we found that exosomal fractions called "apoptotic exosome-like vesicles" (AEVs) prepared from apoptotic-conditioned medium were the main inflammatory factors. These AEVs showed characteristics of exosomes in their size, density, morphology, and protein expression but had unique marker proteins, sphingosine-1-phosphate receptors 1 and 3 (S1PR1 and 3). Their biogenesis was completely dependent on cellular sphingosine-1-phosphate (S1P)/S1PRs signaling from multiple fine spindles of plasma membrane accompanied by F-actin, S1PR1, S1PR3, and CD63 at the early apoptotic phase and progressing to the maturation of F-actin-guided multivesicular endosomes mediated by Gβγ subunits of S1PRs downstream. S1P-loaded S1PRs on AEVs were critical factors for inducing IL-1β via NF-κB transcriptional factor and p38 MAPK, possibly through the RHOA/NOD2 axis, in differentiating macrophages. The AEVs induced genes of proinflammatory cytokines, chemokines, and mediators in both in vitro and in vivo models. In conclusion, AEVs could be key inflammatory mediators, acting as DAMPs that could explain the pathogeneses of various chronic inflammations, autoimmune diseases, or cancers in the future.

Endo-lysosomal sorting of G-protein-coupled receptors by ubiquitin: Diverse pathways for G-protein-coupled receptor destruction and beyond

Ubiquitin is covalently attached to substrate proteins in the form of a single ubiquitin moiety or polyubiquitin chains and has been generally linked to protein degradation, however, distinct types of ubiquitin linkages are also used to control other critical cellular processes like cell signaling. Over forty mammalian G protein-coupled receptors (GPCRs) have been reported to be ubiquitinated, but despite the diverse and rich complexity of GPCR signaling, ubiquitin has been largely ascribed to receptor degradation. Indeed, GPCR ubiquitination targets the receptors for degradation by lysosome, which is mediated by the Endosomal Sorting Complexes Required for Transport (ESCRT) machinery, and the proteasome. This has led to the view that ubiquitin and ESCRTs primarily function as the signal to target GPCRs for destruction. Contrary to this conventional view, studies indicate that ubiquitination of certain GPCRs and canonical ubiquitin-binding ESCRTs are not required for receptor degradation and revealed that diverse and complex pathways exist to regulate endo-lysosomal sorting of GPCRs. In other studies, GPCR ubiquitination has been shown to drive signaling and not receptor degradation and further revealed novel insight into the mechanisms by which GPCRs trigger the activity of the ubiquitination machinery. Here, we discuss the diverse pathways by which ubiquitin controls GPCR endo-lysosomal sorting and beyond.

Compartmentalisation of RAC1 signalling

RAC1 signalling has been implicated in a variety of dynamic cell biological processes that are orchestrated through regulated localisation and activation of RAC1. As a small GTPase, RAC1 switches between active and inactive states at various subcellular locations that include the plasma membrane, nucleus and mitochondria. Once activated, RAC1 interacts with a range of effectors that then mediate various biological functions. RAC1 is regulated by a large number of proteins that can promote its recruitment, activation, deactivation, or stability. RAC1 and its regulators are subject to various post-translational modifications that further fine tune RAC1 localisation, levels and activity. Developments in technologies have enabled the accurate detection of activated RAC1 during processes such as cell migration, invasion and DNA damage. Here, we highlight recent advances in our understanding of RAC1 regulation and function at specific subcellular sites.