Vesicle Size Regulates Nanotube Formation in the Cell

Liensinine overcomes EGFR-TKI resistance in lung adenocarcinoma through DRP1-mediated autophagy

INTRODUCTION

Persistent upregulation of autophagy contributes to tumour cells' resistance to EGFR-TKI therapy, and hence, inhibiting autophagy could be a valuable strategy for overcoming such resistance.

OBJECTIVES

This study investigated the effects of liensinine in EGFR-TKI resistant lung adenocarcinoma (LUAD) and to explore the underlying mechanism.

METHODS

CCK-8 assay, colony formation, EdU assay and apoptosis assays were conducted for investigating the effect of EGFR-TKI and liensinine combination treatment in LUAD. Furthermore, autophagic flux were detected by western blot, fluorescence assays and TEM. In addition, by employing a DARTS approach, a CETSA assay, and SPR analysis, we identified DRP1 as a target of liensinine. Finally, by establishing a xenograft model of the disease, the impact of combination treatment in vivo was assessed.

RESULT

In vitro and in vivo experiments revealed that the novel autophagy inhibitor liensinine enhanced the sensitivity of LUAD to EGFR-TKIs. This effect was achieved by inhibiting autophagic flux. We then examined whether liensinine inhibits autophagic flux through the impairment of autophagosome and autolysosome degradation. Furthermore, we identified DRP1 as a target of liensinine. The activation of DRP1 by liensinine through dephosphorylation at Ser637 promotes the accumulation of autophagosomes and autolysosomes while simultaneously blocking autophagic flux, thereby enhancing the cancer cell-killing effects of EGFR-TKIs.

CONCLUSIONS

Our study validated the efficacy of liensinine in overcoming EGFR-TKI resistance and elucidated the mechanism underlying liensinine's inhibition of autophagy.

Calcium ions promote migrasome formation via Synaptotagmin-1

Migrasomes, organelles crucial for cell communication, undergo distinct stages of nucleation, maturation, and expansion. The regulatory mechanisms of migrasome formation, particularly through biological cues, remain largely unexplored. This study reveals that calcium is essential for migrasome formation. Furthermore, we identify that Synaptotagmin-1 (Syt1), a well-known calcium sensor, is not only enriched in migrasomes but also indispensable for their formation. The calcium-binding ability of Syt1 is key to initiating migrasome formation. The recruitment of Syt1 to migrasome formation sites (MFS) triggers the swelling of MFS into unstable precursors, which are subsequently stabilized through the sequential recruitment of tetraspanins. Our findings reveal how calcium regulates migrasome formation and propose a sequential interaction model involving Syt1 and Tetraspanins in the formation and stabilization of migrasomes.

Cryopreservation of mesenchymal stromal cell-derived extracellular vesicles using trehalose maintains their ability to expand hematopoietic stem cells in vitro

The multitude of clinical trials using mesenchymal stromal cells (MSCs) has underscored their significance as a promising cell source for regenerative therapies. Most studies have however shown that MSCs get entrapped into the microvasculature of lungs, liver and spleen. In addition to intercellular communication, MSCs exert their effects in a paracrine manner by secretion of extracellular vesicles (EVs). The therapeutic effects of MSC-derived EVs have been examined in several diseases such as hepatic failure, liver injury, hematopoiesis etc. Therefore, optimization of cryopreservation strategies for the long-term storage of functional EVs could help in the development of off-the-shelf biologics. The aim of this study was to develop an optimal cryopreservation strategy for the efficient storage of both types of EVs - Microvesicles (MVs) and exosomes, independently, and to further examine the effect of the cryopreserved EVs on the ex vivo expansion of HSCs. MVs and exosomes were separately cryopreserved at different temperatures using PBS or PBS supplemented with trehalose (pTRE), and these cryopreserved EVs were then assessed for their functionality after revival. We found that addition of trehalose during cryopreservation helped in maintaining the morphology and functionality of the EVs, as assessed by their HSC-supportive potential, ability to expand phenotypically defined HSCs and ability to maintain the chemotactic migration potential of the HSCs co-cultured with them. This strategy could prove to be beneficial for facilitating the use of EVs as cell-free ready-to-use biologics for the ex vivo expansion of HSCs and in regenerative medicine.

Lipid Droplet Contacts With Autophagosomes, Lysosomes, and Other Degradative Vesicles

Lipid droplets (LDs) are dynamic fat-storage organelles that interact readily with numerous cellular structures and organelles. A prominent LD contact site is with degradative vesicles such as autophagosomes, lysosomes, autolysosomes, and late endosomes. These contacts support lipid catabolism through the selective autophagy of LDs (i.e., lipophagy) or the recruitment of cytosolic lipases to the LD surface (i.e., lipolysis). However, LD-autophagosome contacts serve additional functions beyond lipid catabolism, including the supply of lipids for autophagosome biogenesis. In this review, we discuss the molecular mediators of LD contacts with autophagosomes and other degradative organelles as well as the diverse cellular functions of these contact sites in health and disease.

Lysosomal size matters

Lysosomes are key cellular catabolic centers that also perform fundamental metabolic, signaling and quality control functions. Lysosomes are not static and they respond dynamically to intra‐ and extracellular stimuli triggering changes in organelle numbers, size and position. Such physical changes have a strong impact on lysosomal activity ultimately influencing cellular homeostasis. In this review, we summarize the current knowledge on lysosomal size regulation, on its physiological role(s) and association to several disease conditions.

Lipid droplet size directs lipolysis and lipophagy catabolism in hepatocytes

Lipid droplet (LD) catabolism in hepatocytes is mediated by a combination of lipolysis and a selective autophagic mechanism called lipophagy, but the relative contributions of these seemingly distinct pathways remain unclear. We find that inhibition of lipolysis, lipophagy, or both resulted in similar overall LD content but dramatic differences in LD morphology. Inhibition of the lipolysis enzyme adipose triglyceride lipase (ATGL) resulted in large cytoplasmic LDs, whereas lysosomal inhibition caused the accumulation of numerous small LDs within the cytoplasm and degradative acidic vesicles. Combined inhibition of ATGL and LAL resulted in large LDs, suggesting that lipolysis targets these LDs upstream of lipophagy. Consistent with this, ATGL was enriched in larger-sized LDs, whereas lipophagic vesicles were restricted to small LDs as revealed by immunofluorescence, electron microscopy, and Western blot of size-separated LDs. These findings provide new evidence indicating a synergistic relationship whereby lipolysis targets larger-sized LDs to produce both size-reduced and nascently synthesized small LDs that are amenable for lipophagic internalization.

Migrasome formation is mediated by assembly of micron-scale tetraspanin macrodomains

Migrasomes are recently discovered cellular organelles that form as large vesicle-like structures on retraction fibres of migrating cells. While the process of migrasome formation has been described before, the molecular mechanism underlying migrasome biogenesis remains unclear. Here, we propose that the mechanism of migrasome formation consists of the assembly of tetraspanin- and cholesterol-enriched membrane microdomains into micron-scale macrodomains, which swell into migrasomes. The major finding underlying the mechanism is that tetraspanins and cholesterol are necessary and sufficient for migrasome formation. We demonstrate the necessity of tetraspanins and cholesterol via live-cell experiments, and their sufficiency by generating migrasome-like structures in reconstituted membrane systems. We substantiate the mechanism by a theoretical model proposing that the key factor driving migrasome formation is the elevated membrane stiffness of the tetraspanin- and cholesterol-enriched macrodomains. Finally, the theoretical model was quantitatively validated by experimental demonstration of the membrane-stiffening effect of tetraspanin 4 and cholesterol.

Single-molecule in vitro reconstitution assay for kinesin-1-driven membrane dynamics

Intracellular membrane dynamics, especially the nano-tube formation, plays important roles in vesicle transportation and organelle biogenesis. Regarding the regulation mechanisms, it is well known that during the nano-tube formation, motor proteins act as the driven force moving along the cytoskeleton, lipid composition and its associated proteins serve as the linkers and key mediators, and the vesicle sizes play as one of the important regulators. In this review, we summarized the in vitro reconstitution assay method, which has been applied to reconstitute the nano-tube dynamics during autophagic lysosomal regeneration (ALR) and the morphology dynamics during mitochondria network formation (MNF) in a mimic and pure in vitro system. Combined with the single-molecule microscopy, the advantage of the in vitro reconstitution system is to study the key questions at a single-molecule or single-vesicle level with precisely tuned parameters and conditions, such as the motor mutation, ion concentration, lipid component, ATP/GTP concentration, and even in vitro protein knockout, which cannot easily be achieved by in vivo or intracellular studies.

Extracellular membrane vesicles in the three domains of life and beyond

Cells from all three domains of life, Archaea, Bacteria and Eukarya, produce extracellular vesicles (EVs) which are sometimes associated with filamentous structures known as nanopods or nanotubes. The mechanisms of EV biogenesis in the three domains remain poorly understood, although studies in Bacteria and Eukarya indicate that the regulation of lipid composition plays a major role in initiating membrane curvature. EVs are increasingly recognized as important mediators of intercellular communication via transfer of a wide variety of molecular cargoes. They have been implicated in many aspects of cell physiology such as stress response, intercellular competition, lateral gene transfer (via RNA or DNA), pathogenicity and detoxification. Their role in various human pathologies and aging has aroused much interest in recent years. EVs can be used as decoys against viral attack but virus-infected cells also produce EVs that boost viral infection. Here, we review current knowledge on EVs in the three domains of life and their interactions with the viral world.

Visualizing Autophagic Lysosome Reformation in Cells Using In Vitro Reconstitution Systems

Autophagy is a lysosome-based degradation pathway. Autophagic lysosome reformation (ALR) is a lysosomal membrane recycling process that marks the terminal step of autophagy. During ALR, LAMP1-positive tubules, named reformation tubules, are extruded from autolysosomes, and nascent lysosomes are generated from these tubules. By combining proteomic analysis of purified autolysosomes and RNA interference screening of identified candidates, we systematically elucidated the ALR pathway at the molecular level. Based on the key components clathrin, PtdIns(4,5)P₂ , and the motor protein KIF5B, among others, we reconstituted this process in vitro. This unit describes a detailed method for visualizing ALR in cells during the autophagy process. This unit also present a protocol for reconstituting the ALR tubular protrusion and elongation process in vitro and three methods for preparing materials for in vitro reconstitution: (1) autolysosome purification from cultured cells, (2) liposome preparation, and (3) KIF5B purification and quality testing. © 2018 by John Wiley & Sons, Inc.

Studying Autophagic Lysosome Reformation in Cells and by an In Vitro Reconstitution System

Autophagic lysosome reformation (ALR) is the terminal step of autophagy. ALR functions to recycle lysosomal membranes and maintain lysosome homeostasis. Maintaining a functional lysosome pool is critical for generating autolysosomes, in which cellular components are degraded and turned over during autophagy. This unit describes methods to visualize ALR in cells. In addition, this unit provides detailed protocols to establish in vitro systems which can be used to reconstitute ALR as well as to reconstitute mitochondrial tubulation/network formation, another process that is driven by motor proteins.

Tracking Lysosome Migration within Chinese Hamster Ovary (CHO) Cells Following Exposure to Nanosecond Pulsed Electric Fields

Above a threshold electric field strength, 600 ns-duration pulsed electric field (nsPEF) exposure substantially porates and permeabilizes cellular plasma membranes in aqueous solution to many small ions. Repetitive exposures increase permeabilization to calcium ions (Ca²⁺) in a dosage-dependent manner. Such exposure conditions can create relatively long-lived pores that reseal after passive lateral diffusion of lipids should have closed the pores. One explanation for eventual pore resealing is active membrane repair, and an ubiquitous repair mechanism in mammalian cells is lysosome exocytosis. A previous study shows that intracellular lysosome movement halts upon a 16.2 kV/cm, 600-ns PEF exposure of a single train of 20 pulses at 5 Hz. In that study, lysosome stagnation qualitatively correlates with the presence of Ca²⁺ in the extracellular solution and with microtubule collapse. The present study tests the hypothesis that limitation of nsPEF-induced Ca²⁺ influx and colloid osmotic cell swelling permits unabated lysosome translocation in exposed cells. The results indicate that the efforts used herein to preclude Ca²⁺ influx and colloid osmotic swelling following nsPEF exposure did not prevent attenuation of lysosome translocation. Intracellular lysosome movement is inhibited by nsPEF exposure(s) in the presence of PEG 300-containing solution or by 20 pulses of nsPEF in the presence of extracellular calcium. The only cases with no significant decreases in lysosome movement are the sham and exposure to a single nsPEF in Ca²⁺-free solution.

Biophysical nanotools for single-molecule dynamics

The focus of the cell biology field is now shifting from characterizing cellular activities to organelle and molecular behaviors. This process accompanies the development of new biophysical visualization techniques that offer high spatial and temporal resolutions with ultra-sensitivity and low cell toxicity. They allow the biology research community to observe dynamic behaviors from scales of single molecules, organelles, cells to organoids, and even live animal tissues. In this review, we summarize these biophysical techniques into two major classes: the mechanical nanotools like dynamic force spectroscopy (DFS) and the optical nanotools like single-molecule and super-resolution microscopy. We also discuss their applications in elucidating molecular dynamics and functionally mapping of interactions between inter-cellular networks and intra-cellular components, which is key to understanding cellular processes such as adhesion, trafficking, inheritance, and division.

Mechanics of cellular packing of nanorods with finite and non-uniform diameters

To understand the mechanics of cellular/intracellular packing of one-dimensional nanomaterials, we performed theoretical analysis and molecular dynamics simulations to investigate how the morphology and mechanical behaviors of a lipid vesicle are regulated by encapsulated rigid nanorods of finite and non-uniform diameters, including a cylindrical rod, a rod with widened ends, a cone-shaped rod, and a screwdriver-shaped rod. As the rod length increases, the vesicle evolves from a sphere into different shapes, such as a lemon, a conga drum, a cherry, a bowling pin, or a tubular shape for long and thick rods. The contact between the vesicle protrusion and the rod plays an important role in regulating the vesicle tubulation, membrane tension, and axial contact force on the rod. Our analysis provides a theoretical basis to understand a wide range of experiments on morphological transitions that occur in cellular packing of actin or microtubule bundles, mitotic cell division, and intracellular packing of carbon nanotubes.

Fibronectin rescues estrogen receptor α from lysosomal degradation in breast cancer cells

Estrogen receptor α (ERα) is expressed in tissues as diverse as brains and mammary glands. In breast cancer, ERα is a key regulator of tumor progression. Therefore, understanding what activates ERα is critical for cancer treatment in particular and cell biology in general. Using biochemical approaches and superresolution microscopy, we show that estrogen drives membrane ERα into endosomes in breast cancer cells and that its fate is determined by the presence of fibronectin (FN) in the extracellular matrix; it is trafficked to lysosomes in the absence of FN and avoids the lysosomal compartment in its presence. In this context, FN prolongs ERα half-life and strengthens its transcriptional activity. We show that ERα is associated with β1-integrin at the membrane, and this integrin follows the same endocytosis and subcellular trafficking pathway triggered by estrogen. Moreover, ERα⁺ vesicles are present within human breast tissues, and colocalization with β1-integrin is detected primarily in tumors. Our work unravels a key, clinically relevant mechanism of microenvironmental regulation of ERα signaling.

Development of Research into Autophagic Lysosome Reformation

Autophagy is a lysosome-dependent degradation process that is essential for maintaining cellular homeostasis. In recent years, more studies have focused on the late stages of autophagy. Our group discovered and studied the terminal step of autophagy, namely autophagic lysosome reformation (ALR). ALR is the process that regenerates functional lysosomes from autolysosomes, thus maintaining lysosome homeostasis. ALR involves clathrin-mediated membrane budding from autolysosomes, elongation of membrane tubules along microtubules with the pulling force provided by the motor protein KIF5B, proto-lysosome scission by dynamin 2, and finally maturation of proto-lysosomes to functional lysosomes. In this review, we will summarize progress in unveiling the molecular mechanisms underlying ALR and its potential pathophysiological roles.

Viral highway to nucleus exposed by image correlation analyses

Parvoviral genome translocation from the plasma membrane into the nucleus is a coordinated multistep process mediated by capsid proteins. We used fast confocal microscopy line scan imaging combined with image correlation methods including auto-, pair- and cross-correlation, and number and brightness analysis, to study the parvovirus entry pathway at the single-particle level in living cells. Our results show that the endosome-associated movement of virus particles fluctuates from fast to slow. Fast transit of single cytoplasmic capsids to the nuclear envelope is followed by slow movement of capsids and fast diffusion of capsid fragments in the nucleoplasm. The unique combination of image analyses allowed us to follow the fate of intracellular single virus particles and their interactions with importin β revealing previously unknown dynamics of the entry pathway.

Liposomally formulated phospholipid-conjugated novel near-infrared fluorescence probe for particle size effect on cellular uptake and biodistribution in vivo

Lipid based nanoparticles (LBNs) with excellent biocompatibility and versatility have received much attention from the drug delivery community recently. A detailed understanding of in vitro and vivo fate of LBNs is important for developing different types of LBNs with improved selectivity and low cytotoxicity. We developed a novel near-infrared (NIR) probe with high fluorescence, designated as DSPE-ir623 (iDSPE). Then, we prepared iDSPE-embeded liposomes (iLPs) with two different hydrodynamic sizes (∼100nm and ∼400nm) to evaluate the effect of particle size on cellular uptake and biodistribution of nanoliposomes in vivo. These iLPs were proved to exhibit good monodispersity, excellent fluorescence and stability. In vitro cell uptake tests demonstrated that iLPs-1 (∼100nm) were taken up more by HT-29 cells than iLPs-2 (∼400nm). Notably, the fluorescence of iLPs can be employed for real-time monitoring of the subcellular locating and its metabolic distribution in vivo. Near-infrared imaging in vivo illustrated that iLPs-1 was mainly accumulated in the tumor tissues, while iLPs-2 was accumulated in liver and spleen. The results indicated that the size of iLPs play an important role in the regulation of intracellular trafficking and biodistribution of liposomes, which also provide a new insight into the development of more effective LBNs. Hence, iDSPE might be a promising tool for the reliable tracing of different types of LBNs.

Liposomally formulated phospholipid-conjugated novel near-infrared fluorescence probe for particle size effect on cellular uptake and biodistribution in vivo

Lipid based nanoparticles (LBNs) with excellent biocompatibility and versatility have received much attention from the drug delivery community recently. A detailed understanding of in vitro and vivo fate of LBNs is important for developing different types of LBNs with improved selectivity and low cytotoxicity. We developed a novel near-infrared (NIR) probe with high fluorescence, designated as DSPE-ir623 (iDSPE). Then, we prepared iDSPE-embeded liposomes (iLPs) with two different hydrodynamic sizes (∼100nm and ∼400nm) to evaluate the effect of particle size on cellular uptake and biodistribution of nanoliposomes in vivo. These iLPs were proved to exhibit good monodispersity, excellent fluorescence and stability. In vitro cell uptake tests demonstrated that iLPs-1 (∼100nm) were taken up more by HT-29 cells than iLPs-2 (∼400nm). Notably, the fluorescence of iLPs can be employed for real-time monitoring of the subcellular locating and its metabolic distribution in vivo. Near-infrared imaging in vivo illustrated that iLPs-1 was mainly accumulated in the tumor tissues, while iLPs-2 was accumulated in liver and spleen. The results indicated that the size of iLPs play an important role in the regulation of intracellular trafficking and biodistribution of liposomes, which also provide a new insight into the development of more effective LBNs. Hence, iDSPE might be a promising tool for the reliable tracing of different types of LBNs.

Protoparvovirus Knocking at the Nuclear Door

Protoparvoviruses target the nucleus due to their dependence on the cellular reproduction machinery during the replication and expression of their single-stranded DNA genome. In recent years, our understanding of the multistep process of the capsid nuclear import has improved, and led to the discovery of unique viral nuclear entry strategies. Preceded by endosomal transport, endosomal escape and microtubule-mediated movement to the vicinity of the nuclear envelope, the protoparvoviruses interact with the nuclear pore complexes. The capsids are transported actively across the nuclear pore complexes using nuclear import receptors. The nuclear import is sometimes accompanied by structural changes in the nuclear envelope, and is completed by intranuclear disassembly of capsids and chromatinization of the viral genome. This review discusses the nuclear import strategies of protoparvoviruses and describes its dynamics comprising active and passive movement, and directed and diffusive motion of capsids in the molecularly crowded environment of the cell.

Kinesin 1 Drives Autolysosome Tubulation

Autophagic lysosome reformation (ALR) plays an important role in maintaining lysosome homeostasis. During ALR, lysosomes are reformed by recycling lysosomal components from autolysosomes. The most noticeable step of ALR is autolysosome tubulation, but it is currently unknown how the process is regulated. Here, using an approach combining in vivo studies and in vitro reconstitution, we found that the kinesin motor protein KIF5B is required for autolysosome tubulation and that KIF5B drives autolysosome tubulation by pulling on the autolysosomal membrane. Furthermore, we show that KIF5B directly interacts with PtdIns(4,5)P2. Kinesin motors are recruited and clustered on autolysosomes via interaction with PtdIns(4,5)P2 in a clathrin-dependent manner. Finally, we demonstrate that clathrin promotes formation of PtdIns(4,5)P2-enriched microdomains, which are required for clustering of KIF5B. Our study reveals a mechanism by which autolysosome tubulation was generated.

Recent progress in autophagic lysosome reformation

Autophagic lysosome reformation (ALR) is the terminal step of autophagy and is essential for maintaining lysosome homeostasis during autophagy. During ALR, tubules are extruded from autolysosomes, and small vesicles named proto-lysosomes, which are composed of lysosomal membrane components, are generated from these tubules. Eventually, proto-lysosomes mature into functional lysosomes. In this review, we will summarize recent progress in understanding the regulation, mechanisms and physiological functions of ALR.