Pacsin 2-dependent N-cadherin internalization regulates the migration behaviour of malignant cancer cells.

Collective cell migration is the coordinated movement of multiple cells connected by cadherin-based adherens junctions and is essential for physiological and pathological processes. Cadherins undergo dynamic intracellular trafficking, and their surface level is determined by a balance between endocytosis, recycling and degradation. However, the regulatory mechanism of cadherin turnover in collective cell migration remains elusive. In this study, we show that the Bin/amphiphysin/Rvs (BAR) domain protein pacsin 2 (protein kinase C and casein kinase substrate in neurons protein 2) plays an essential role in collective cell migration by regulating N-cadherin (also known as CDH2) endocytosis in human cancer cells. Pacsin 2-depleted cells formed cell-cell contacts enriched with N-cadherin and migrated in a directed manner. Furthermore, pacsin 2-depleted cells showed attenuated internalization of N-cadherin from the cell surface. Interestingly, GST pull-down assays demonstrated that the pacsin 2 SH3 domain binds to the cytoplasmic region of N-cadherin, and expression of an N-cadherin mutant defective in binding to pacsin 2 phenocopied pacsin 2 RNAi cells both in cell contact formation and N-cadherin endocytosis. These data support new insights into a novel endocytic route of N-cadherin in collective cell migration, highlighting pacsin 2 as a possible therapeutic target for cancer metastasis.

Structural basis of Irgb6 inactivation by Toxoplasma gondii through the phosphorylation of switch I.

Irgb6 is a priming immune-related GTPase (IRG) that counteracts Toxoplasma gondii. It is known to be recruited to the low virulent type II T. gondii parasitophorous vacuole (PV), initiating cell-autonomous immunity. However, the molecular mechanism by which immunity-related GTPases become inactivated after the parasite infection remains obscure. Here, we found that Thr95 of Irgb6 is prominently phosphorylated in response to low virulent type II T. gondii infection. We observed that a phosphomimetic T95D mutation in Irgb6 impaired its localization to the PV and exhibited reduced GTPase activity in vitro. Structural analysis unveiled an atypical conformation of nucleotide-free Irgb6-T95D, resulting from a conformational change in the G-domain that allosterically modified the PV membrane-binding interface. In silico docking corroborated the disruption of the physiological membrane binding site. These findings provide novel insights into a T. gondii-induced allosteric inactivation mechanism of Irgb6.

Imaging-based evaluation of pathogenicity by novel DNM2 variants associated with centronuclear myopathy.

A centronuclear myopathy (CNM) is a group of inherited congenital diseases showing clinically progressive muscle weakness associated with the presence of centralized myonuclei, diagnosed by genetic testing and muscle biopsy. The gene encoding dynamin 2, DNM2, has been identified as a causative gene for an autosomal dominant form of CNM. However, the information of a DNM2 variant alone is not always sufficient to gain a definitive diagnosis as the pathogenicity of many gene variants is currently unknown. In this study, we identified five novel DNM2 variants in our cohort. To establish the pathogenicity of these variants without using clinicopathological information, we used a simple in cellulo imaging-based assay for T-tubule-like structures to provide quantitative data that enable objective determination of pathogenicity by novel DNM2 variants. With this assay, we demonstrated that the phenotypes induced by mutant dynamin 2 in cellulo are well correlated with biochemical gain-of-function features of mutant dynamin 2 as well as the clinicopathological phenotypes of each patient. Our approach of combining an in cellulo assay with clinical information of the patients also explains the course of a disease progression by the pathogenesis of each variant in DNM2-associated CNM.

Mutant BIN1-Dynamin 2 complexes dysregulate membrane remodeling in the pathogenesis of centronuclear myopathy.

Membrane remodeling is required for dynamic cellular processes such as cell division, polarization, and motility. BAR domain proteins and dynamins are key molecules in membrane remodeling that work together for membrane deformation and fission. In striated muscles, sarcolemmal invaginations termed T-tubules are required for excitation-contraction coupling. BIN1 and DNM2, which encode a BAR domain protein BIN1 and dynamin 2, respectively, have been reported to be causative genes of centronuclear myopathy (CNM), a hereditary degenerative disease of skeletal muscle, and deformation of T-tubules is often observed in the CNM patients. However, it remains unclear how BIN1 and dynamin 2 are implicated in T-tubule biogenesis and how mutations in these molecules cause CNM to develop. Here, using an in cellulo reconstitution assay, we demonstrate that dynamin 2 is required for stabilization of membranous structures equivalent to T-tubules. GTPase activity of wild-type dynamin 2 is suppressed through interaction with BIN1, whereas that of the disease-associated mutant dynamin 2 remains active due to lack of the BIN1-mediated regulation, thus causing aberrant membrane remodeling. Finally, we show that in cellulo aberrant membrane remodeling by mutant dynamin 2 variants is correlated with their enhanced membrane fission activities, and the results can explain severity of the symptoms in patients. Thus, this study provides molecular insights into dysregulated membrane remodeling triggering the pathogenesis of DNM2-related CNM.

Dynamin 2 and BAR domain protein pacsin 2 cooperatively regulate formation and maturation of podosomes.

Podosomes are actin-rich adhesion structures formed in a variety of cell types, such as monocytic cells or cancer cells, to facilitate attachment to and degradation of the extracellular matrix (ECM). Previous studies showed that dynamin 2, a large GTPase involved in membrane remodeling and actin organization, is required for podosome function. However, precise roles of dynamin 2 at the podosomes remain to be elucidated. In this study, we identified a BAR (Bin-Amphiphysin-Rvs167) domain protein pacsin 2 as a functional partner of dynamin 2 at podosomes. Dynamin 2 and pacsin 2 interact and co-localize to podosomes in Src-transformed NIH 3T3 (NIH-Src) cells. RNAi of either dynamin 2 or pacsin 2 in NIH-Src cells inhibited podosome formation and maturation, suggesting essential and related roles at podosomes. Consistently, RNAi of pacsin 2 prevented dynamin 2 localization to podosomes, and reciprocal RNAi of dynamin 2 prevented pacsin 2 localization to podosomes. Taking these results together, we conclude that dynamin 2 and pacsin 2 co-operatively regulate organization of podosomes in NIH-Src cells.

Dynamin 1 is important for microtubule organization and stabilization in glomerular podocytes.

Dynamin 1 is a neuronal endocytic protein that participates in vesicle formation by scission of invaginated membranes. Dynamin 1 is also expressed in the kidney; however, its physiological significance to this organ remains unknown. Here, we show that dynamin 1 is crucial for microtubule organization and stabilization in glomerular podocytes. By immunofluorescence and immunoelectron microscopy, dynamin 1 was concentrated at microtubules at primary processes in rat podocytes. By immunofluorescence of differentiated mouse podocytes (MPCs), dynamin 1 was often colocalized with microtubule bundles, which radially arranged toward periphery of expanded podocyte. In dynamin 1-depleted MPCs by RNAi, α-tubulin showed a dispersed linear filament-like localization, and microtubule bundles were rarely observed. Furthermore, dynamin 1 depletion resulted in the formation of discontinuous, short acetylated α-tubulin fragments, and the decrease of microtubule-rich protrusions. Dynamins 1 and 2 double-knockout podocytes showed dispersed acetylated α-tubulin and rare protrusions. In vitro, dynamin 1 polymerized around microtubules and cross-linked them into bundles, and increased their resistance to the disassembly-inducing reagents Ca2+ and podophyllotoxin. In addition, overexpression and depletion of dynamin 1 in MPCs increased and decreased the nocodazole resistance of microtubules, respectively. These results suggest that dynamin 1 supports the microtubule bundle formation and participates in the stabilization of microtubules.

Internalization of AMPA-type Glutamate Receptor in the MIN6 Pancreatic ß-cell Line.

The activity of AMPA-type glutamate receptor is involved in insulin release from pancreatic ß-cells. However, the mechanism and dynamics that underlie AMPA receptor-mediated insulin release in ß-cells is largely unknown. Here, we show that AMPA induces internalization of glutamate receptor 2/3 (GluR2/3), AMPA receptor subtype, in the mouse ß-cell line MIN6. Immunofluorescence experiments showed that GluR2/3 appeared as fine dots that were distributed throughout MIN6 cells. Intracellular GluR2/3 co-localized with AP2 and clathrin, markers for clathrin-coated pits and vesicles. Immunoelectron microscopy revealed that GluR2/3 was also localized at plasma membrane. Surface biotinylation and immunofluorescence measurements showed that addition of AMPA caused an approximate 1.8-fold increase in GluR2/3 internalization under low-glucose conditions. Furthermore, internalized GluR2 largely co-localized with EEA1, an early endosome marker. In addition, GluR2/3 co-immunoprecipitated with cortactin, a F-actin binding protein. Depletion of cortactin by RNAi in MIN6 cells altered the intracellular distribution of GluR2/3, suggesting that cortactin is involved in internalization of GluR2/3 in MIN6 cells. Taken together, our results suggest that pancreatic ß-cells adjust the amount of AMPA-type GluR2/3 on the cell surface to regulate the receptive capability of the cell for glutamate.Key words: endocytosis, GluR2, AMPA, cortactin, MIN6.

Phosphatidic acid induces EHD3-containing membrane tubulation and is required for receptor recycling.

EHD3 is localized on the tubular structures of early endosomes, and it regulates their trafficking pathway. However, the regulatory mechanism of EHD3-containing tubular structures remains poorly understood. An in vitro liposome co-sedimentation assay revealed that EHD3 interacted with phosphatidic acid through its helical domain and this interaction induced liposomal tubulations. Additionally, inhibiting phosphatidic acid synthesis with diacylglycerol kinase inhibitor or lysophosphatidic acid acyltransferase inhibitor significantly reduced the number of EHD3-containing tubules and impaired their trafficking from early endosomes. These results suggest that EHD3 and phosphatidic acid cooperatively regulate membrane deformation and trafficking from early endosomes.

Dynamin2 GTPase contributes to invadopodia formation in invasive bladder cancer cells.

Cancer cell invasion is mediated by actin-based membrane protrusions termed invadopodia. Invadopodia consist of "core" F-actin bundles associated with adhesive and proteolytic machineries promoting cell invasion by degrading extracellular matrix (ECM). Formation of the F-actin core in invadopodia is regulated by various actin-binding proteins including Arp2/3 complex and cortactin. Dynamin GTPase localizes to the invadopodia and is implicated in cancer cell invasion, but its precise role at the invadopodia remained elusive. In this study, we examined the roles of dynamin at the invadopodia of bladder cancer cells. Although all three dynamin isoforms (dynamin1, 2 and 3) are expressed in human bladder cancer cell line T24, only dynamin2 localizes to the invadopodia. Inhibition of dynamin2 function, using either RNA interference (RNAi) or the dynamin specific inhibitor Dynasore, caused defects in invadopodia formation and suppressed invasive activity of T24 bladder cancer cells. Structure-function analysis using dynamin2 deletion fragments identified the proline/arginine-rich domain (PRD) of dynamin2 as indispensable for invadopodia formation and invasiveness of T24 cells. Thus, dynamin2 contributes to bladder cancer invasion by controlling invadopodia formation in bladder cancer cells and may prove a valuable therapeutic target.

Possible role of cortactin phosphorylation by protein kinase Cα in actin-bundle formation at growth cone.

BACKGROUND INFORMATION: Cortactin contributes to growth cone morphogenesis by forming with dynamin, ring-shaped complexes that mechanically bundle and stabilise F-actin. However, the regulatory mechanism of cortactin action is poorly understood. RESULTS: Immunofluorescence microscopy revealed that protein kinase C (PKC) α colocalises with cortactin at growth cone filopodia in SH-SY5Y neuroblastoma cells. PKC activation by phorbol 12-myristate 13-acetate causes cortactin phosphorylation, filopodial retraction and F-actin-bundle loss. Moreover, PKCα directly phosphorylates cortactin in vitro at S135/T145/S172, mitigating both cortactin's actin-binding and actin-crosslinking activity, whereas cellular expression of a phosphorylation-mimetic cortactin mutant hinders filopodial formation with a significant decrease of actin bundles. CONCLUSIONS: Our results indicate that PKC-mediated cortactin phosphorylation might be implicated in the maintenance of growth cone.

Stabilization of actin bundles by a dynamin 1/cortactin ring complex is necessary for growth cone filopodia.

Dynamin GTPase, a key molecule in endocytosis, mechanically severs the invaginated membrane upon GTP hydrolysis. Dynamin functions also in regulating actin cytoskeleton, but the mechanisms are yet to be defined. Here we show that dynamin 1, a neuronal isoform of dynamin, and cortactin form ring complexes, which twine around F-actin bundles and stabilize them. By negative-staining EM, dynamin 1-cortactin complexes appeared as "open" or "closed" rings depending on guanine nucleotide conditions. By pyrene actin assembly assay, dynamin 1 stimulated actin assembly in mouse brain cytosol. In vitro incubation of F-actin with both dynamin 1 and cortactin led to the formation of long and thick actin bundles, on which dynamin 1 and cortactin were periodically colocalized in puncta. A depolymerization assay revealed that dynamin 1 and cortactin increased the stability of actin bundles, most prominently in the presence of GTP. In rat cortical neurons and human neuroblastoma cell line, SH-SY5Y, both dynamin 1 and cortactin localized on actin filaments and the bundles at growth cone filopodia as revealed by immunoelectron microscopy. In SH-SY5Y cell, acute inhibition of dynamin 1 by application of dynamin inhibitor led to growth cone collapse. Cortactin knockdown also reduced growth cone filopodia. Together, our results strongly suggest that dynamin 1 and cortactin ring complex mechanically stabilizes F-actin bundles in growth cone filopodia. Thus, the GTPase-dependent mechanochemical enzyme property of dynamin is commonly used both in endocytosis and regulation of F-actin bundles by a dynamin 1-cortactin complex.

Metallothionein deficiency exacerbates diabetic nephropathy in streptozotocin-induced diabetic mice.

Oxidative stress and inflammation play important roles in diabetic complications, including diabetic nephropathy. Metallothionein (MT) is induced in proximal tubular epithelial cells as an antioxidant in the diabetic kidney; however, the role of MT in renal function remains unclear. We therefore investigated whether MT deficiency accelerates diabetic nephropathy through oxidative stress and inflammation. Diabetes was induced by streptozotocin injection in MT-deficient (MT(-/-)) and MT(+/+) mice. Urinary albumin excretion, histological changes, markers for reactive oxygen species (ROS), and kidney inflammation were measured. Murine proximal tubular epithelial (mProx24) cells were used to further elucidate the role of MT under high-glucose conditions. Parameters of diabetic nephropathy and markers of ROS and inflammation were accelerated in diabetic MT(-/-) mice compared with diabetic MT(+/+) mice, despite equivalent levels of hyperglycemia. MT deficiency accelerated interstitial fibrosis and macrophage infiltration into the interstitium in the diabetic kidney. Electron microscopy revealed abnormal mitochondrial morphology in proximal tubular epithelial cells in diabetic MT(-/-) mice. In vitro studies demonstrated that knockdown of MT by small interfering RNA enhanced mitochondrial ROS generation and inflammation-related gene expression in mProx24 cells cultured under high-glucose conditions. The results of this study suggest that MT may play a key role in protecting the kidney against high glucose-induced ROS and subsequent inflammation in diabetic nephropathy.

N'-[4-(dipropylamino)benzylidene]-2-hydroxybenzohydrazide is a dynamin GTPase inhibitor that suppresses cancer cell migration and invasion by inhibiting actin polymerization.

Dynasore, a specific dynamin GTPase inhibitor, suppresses lamellipodia formation and cancer cell invasion by destabilizing actin filaments. In search for novel dynamin inhibitors that suppress actin dynamics more efficiently, dynasore analogues were screened. N'-[4-(dipropylamino)benzylidene]-2-hydroxybenzohydrazide (DBHA) markedly reduced in vitro actin polymerization, and dose-dependently inhibited phosphatidylserine-stimulated dynamin GTPase activity. DBHA significantly suppressed both the recruitment of dynamin 2 to the leading edge in U2OS cells and ruffle formation in H1299 cells. Furthermore, DBHA suppressed both the migration and invasion of H1299 cells by approximately 70%. Furthermore, intratumoral DBHA delivery significantly repressed tumor growth. DBHA was much less cytotoxic than dynasore. These results strongly suggest that DBHA inhibits dynamin-dependent actin polymerization by altering the interactions between dynamin and lipid membranes. DBHA and its derivative may be potential candidates for potent anti-cancer drugs.

The microtubule-dynamin binding inhibitor peptide PHDP5 rescues spatial learning and memory deficits in Alzheimer's disease model mice.

Dynamin is a microtubule (MT) binding protein playing a key role in vesicle endocytosis. In a brain slice model, tau loaded in presynaptic terminals assembles MTs, thereby impairing vesicle endocytosis via depletion of cytosolic dynamin. The peptide PHDP5, derived from the pleckstrin homology domain of dynamin 1, inhibits dynamin-MT interaction and rescues endocytosis and synaptic transmission impaired by tau when co-loaded in presynaptic terminals. We tested whether in vivo administration of PHDP5 could rescue the learning/memory deficits observed in Alzheimer's disease (AD) model mice. A modified PHDP5 incorporating a cell-penetrating peptide (CPP) and a FITC fluorescent marker was delivered intranasally to Tau609 transgenic (Tg) and 3xTg-AD mice. FITC-positive puncta were observed in the hippocampus of mice infused with PHDP5 or scrambled (SPHDP5) peptide, but not in saline-infused controls. In the Morris water maze (MWM) test for spatial learning/memory, AD model mice treated with FITC-PHDP5-CPP showed prominent improvements in learning and memory, performing close to the level of saline-infused WT mice control. In contrast, mice treated with a scrambled construct (FITC-SPHDP5-CPP) showed no significant improvement. We conclude that PHDP5 can be a candidate for human AD therapy.

Dynamin 2 in Charcot-Marie-Tooth disease.

Charcot-Marie-Tooth disease (CMT) is an inherited neuronal disorder, and is induced by mutations of various genes associated with intracellular membrane traffic and cytoskeleton. A large GTPase, dynamin, which is known as a fission protein for endocytic vesicles, was identified as a gene responsible for dominant-intermediate CMT type 2B (DI-CMT2B). Of these mutants, the PH domain, which is required for interaction with phosphoinositides, was mutated in several families. Interestingly, the expression of a deletion mutant, 551Δ3, did not impair endocytosis, but induced abnormal accumulation of microtubules. Recent evidence has shown that dynamin 2 regulates the dynamic instability of microtubules, and 551Δ3 lacks this function. We propose a model for the regulation of the dynamic instability of microtubules by dynamin 2 and discuss the relationship between dynamin 2 and CMT.

Recruitment of Irgb6 to the membrane is a direct trigger for membrane deformation.

Irgb6 is a member of interferon γ-induced immunity related GTPase (IRG), and one of twenty "effector" IRGs, which coordinately attack parasitophorous vacuole membrane (PVM), causing death of intracellular pathogen. Although Irgb6 plays a pivotal role as a pioneer in the process of PVM disruption, the direct effect of Irgb6 on membrane remained to be elucidated. Here, we utilized artificial lipid membranes to reconstitute Irgb6-membrane interaction in vitro, and revealed that Irgb6 directly deformed the membranes. Liposomes incubated with recombinant Irgb6 were drastically deformed generating massive tubular protrusions in the absence of guanine nucleotide, or with GMP-PNP. Liposome deformation was abolished by incubating with Irgb6-K275A/R371A, point mutations at membrane targeting residues. The membrane tubules generated by Irgb6 were mostly disappeared by the addition of GTP or GDP, which are caused by detachment of Irgb6 from membrane. Binding of Irgb6 to the membrane, which was reconstituted in vitro using lipid monolayer, was stimulated at GTP-bound state. Irgb6 GTPase activity was stimulated by the presence of liposomes more than eightfold. Irgb6 GTPase activity in the absence of membrane was also slightly stimulated, by lowering ionic strength, or by increasing protein concentration, indicating synergistic stimulation of the GTPase activity. These results suggest that membrane targeting of Irgb6 and resulting membrane deformation does not require GTP, but converting into GTP-bound state is crucial for detaching Irgb6 from the membrane, which might coincident with local membrane disruption.

Microtubule assembly by tau impairs endocytosis and neurotransmission via dynamin sequestration in Alzheimer's disease synapse model.

Elevation of soluble wild-type (WT) tau occurs in synaptic compartments in Alzheimer's disease. We addressed whether tau elevation affects synaptic transmission at the calyx of Held in slices from mice brainstem. Whole-cell loading of WT human tau (h-tau) in presynaptic terminals at 10-20 µM caused microtubule (MT) assembly and activity-dependent rundown of excitatory neurotransmission. Capacitance measurements revealed that the primary target of WT h-tau is vesicle endocytosis. Blocking MT assembly using nocodazole prevented tau-induced impairments of endocytosis and neurotransmission. Immunofluorescence imaging analyses revealed that MT assembly by WT h-tau loading was associated with an increased MT-bound fraction of the endocytic protein dynamin. A synthetic dodecapeptide corresponding to dynamin 1-pleckstrin-homology domain inhibited MT-dynamin interaction and rescued tau-induced impairments of endocytosis and neurotransmission. We conclude that elevation of presynaptic WT tau induces de novo assembly of MTs, thereby sequestering free dynamins. As a result, endocytosis and subsequent vesicle replenishment are impaired, causing activity-dependent rundown of neurotransmission.

The Lipid-Binding Defective Dynamin 2 Mutant in Charcot-Marie-Tooth Disease Impairs Proper Actin Bundling and Actin Organization in Glomerular Podocytes.

Dynamin is an endocytic protein that functions in vesicle formation by scission of invaginated membranes. Dynamin maintains the structure of foot processes in glomerular podocytes by directly and indirectly interacting with actin filaments. However, molecular mechanisms underlying dynamin-mediated actin regulation are largely unknown. Here, biochemical and cell biological experiments were conducted to uncover how dynamin modulates interactions between membranes and actin in human podocytes. Actin-bundling, membrane tubulating, and GTPase activities of dynamin were examined in vitro using recombinant dynamin 2-wild-type (WT) or dynamin 2-K562E, which is a mutant found in Charcot-Marie-Tooth patients. Dynamin 2-WT and dynamin 2-K562E led to the formation of prominent actin bundles with constant diameters. Whereas liposomes incubated with dynamin 2-WT resulted in tubule formation, dynamin 2-K562E reduced tubulation. Actin filaments and liposomes stimulated dynamin 2-WT GTPase activity by 6- and 20-fold, respectively. Actin-filaments, but not liposomes, stimulated dynamin 2-K562E GTPase activity by 4-fold. Self-assembly-dependent GTPase activity of dynamin 2-K562E was reduced to one-third compared to that of dynamin 2-WT. Incubation of liposomes and actin with dynamin 2-WT led to the formation of thick actin bundles, which often bound to liposomes. The interaction between lipid membranes and actin bundles by dynamin 2-K562E was lower than that by dynamin 2-WT. Dynamin 2-WT partially colocalized with stress fibers and actin bundles based on double immunofluorescence of human podocytes. Dynamin 2-K562E expression resulted in decreased stress fiber density and the formation of aberrant actin clusters. Dynamin 2-K562E colocalized with α-actinin-4 in aberrant actin clusters. Reformation of stress fibers after cytochalasin D-induced actin depolymerization and washout was less effective in dynamin 2-K562E-expressing cells than that in dynamin 2-WT. Bis-T-23, a dynamin self-assembly enhancer, was unable to rescue the decreased focal adhesion numbers and reduced stress fiber density induced by dynamin 2-K562E expression. These results suggest that the low affinity of the K562E mutant for lipid membranes, and atypical self-assembling properties, lead to actin disorganization in HPCs. Moreover, lipid-binding and self-assembly of dynamin 2 along actin filaments are required for podocyte morphology and functions. Finally, dynamin 2-mediated interactions between actin and membranes are critical for actin bundle formation in HPCs.

Dynamin 2 associates with microtubules at mitosis and regulates cell cycle progression.

Dynamin, a ~100 kDa large GTPase, is known as a key player for membrane traffic. Recent evidence shows that dynamin also regulates the dynamic instability of microtubules by a mechanism independent of membrane traffic. As microtubules are highly dynamic during mitosis, we investigated whether the regulation of microtubules by dynamin is essential for cell cycle progression. Dynamin 2 intensely localized at the mitotic spindle, and the localization depended on its proline-rich domain (PRD), which is required for microtubule association. The deletion of PRD resulted in the impairment of cytokinesis, whereby the mutant had less effect on endocytosis. Interestingly, dominant-negative dynamin (K44A), which blocks membrane traffic but has no effect on microtubules, also blocked cytokinesis. On the other hand, the deletion of the middle domain, which binds to γ-tubulin, impaired the entry into mitosis. As both deletion mutants had no significant effect on endocytosis, dynamin 2 may participate in cell cycle progression by regulating the microtubules. These data suggest that dynamin may play a key role for cell cycle progression by two distinct pathways, membrane traffic and cytoskeleton.

JRAB/MICAL-L2 undergoes liquid-liquid phase separation to form tubular recycling endosomes.

Elongated tubular endosomes play essential roles in diverse cellular functions. Multiple molecules have been implicated in tubulation of recycling endosomes, but the mechanism of endosomal tubule biogenesis has remained unclear. In this study, we found that JRAB/MICAL-L2 induces endosomal tubulation via activated Rab8A. In association with Rab8A, JRAB/MICAL-L2 adopts its closed form, which functions in the tubulation of recycling endosomes. Moreover, JRAB/MICAL-L2 induces liquid-liquid phase separation, initiating the formation of tubular recycling endosomes upon overexpression. Between its N-terminal and C-terminal globular domains, JRAB/MICAL-L2 contains an intrinsically disordered region, which contributes to the formation of JRAB/MICAL-L2 condensates. Based on our findings, we propose that JRAB/MICAL-L2 plays two sequential roles in the biogenesis of tubular recycling endosomes: first, JRAB/MICAL-L2 organizes phase separation, and then the closed form of JRAB/MICAL-L2 formed by interaction with Rab8A promotes endosomal tubulation.