Transient Acceleration of Epidermal Growth Factor Receptor Dynamics Produces Higher-Order Signaling Clusters

Cholesterol suppresses spontaneous activation of EGFR-mediated signal transduction

Epidermal growth factor receptor (EGFR)-mediated signal transduction controls cell growth and proliferation. The signaling pathway is regulated so that it is activated only by external EGF stimuli, but the mechanisms that prevent EGF-independent spontaneous activation of EGFR-mediated signaling are unknown. Here we report cholesterol depletion activates EGFR-mediated signaling without EGF. We applied automated single-molecule imaging to EGFR and characterized the lateral diffusion and cluster formation on cholesterol-depleted and cholesterol-supplemented membranes. In cells in which cholesterol was depleted by methyl-β-cyclodextrin (MβCD) treatment, EGFR exhibited a reduction in lateral diffusion, an acceleration of cluster formation, and autophosphorylation without EGF. Concurrently, extracellular signal-regulated kinase (ERK), which is regulated by EGFR-mediated signaling, exhibited phosphorylation and nuclear translocation without EGF. These cholesterol depletion-induced changes were similar, albeit less efficient, to those that occurred with EGF stimulation in normal cells without MβCD, indicating the spontaneous activation of EGFR signaling. The exogenous supplementation of cholesterol suppressed the MβCD-induced spontaneous activation of EGFR and ERK nuclear translocation. Single-molecule imaging of EGFR in a large number of cells revealed cell-to-cell heterogeneity, with a sub-population showing a high ability for spontaneous activation. These results provide evidence that EGFR-mediated signaling is properly regulated by cholesterol metabolism to prevent uncontrolled spontaneous activation.

TRPV4-dependent Ca2+ influx determines cholesterol dynamics at the plasma membrane

The activities of the transient receptor potential vanilloid 4 (TRPV4), a Ca2+-permeable nonselective cation channel, are controlled by its surrounding membrane lipids (e.g., cholesterol, phosphoinositides). The transmembrane region of TRPV4 contains a cholesterol recognition amino acid consensus (CRAC) motif and its inverted (CARC) motif located in the plasmalemmal cytosolic leaflet. TRPV4 localizes in caveolae, a bulb-shaped cholesterol-rich domain at the plasma membrane. Here, we visualized the spatiotemporal interactions between TRPV4 and cholesterol at the plasma membrane in living cells by dual-color single-molecule imaging using total internal reflection fluorescence microscopy. To this aim, we labeled cholesterol at the cytosolic leaflets of the plasma membrane using a cholesterol biosensor, D4H. Our single-molecule tracking analysis showed that the TRPV4 molecules colocalize with D4H-accessible cholesterol molecules mainly in the low fluidity membrane domains in which both molecules are highly clustered. Colocalization of TRPV4 and D4H-accessible cholesterol was observed both inside and outside of caveolae. Agonist-evoked TRPV4 activation remarkably decreased colocalization probability and association rate between TRPV4 and D4H-accessible cholesterol molecules. Interestingly, upon TRPV4 activation, the particle density of D4H-accessible cholesterol molecules was decreased and the D4H-accessible cholesterol molecules in the fast-diffusing state were increased at the plasma membrane. The introduction of skeletal dysplasia-associated R616Q mutation into the CRAC/CARC motif of TRPV4, which reduced the interaction with cholesterol clusters, could not alter the D4H-accessible cholesterol dynamics. Mechanistically, TRPV4-mediated Ca2+ influx and the C-terminal calmodulin-binding site of TRPV4 are essential for modulating the plasmalemmal D4H-accessible cholesterol dynamics. We propose that TRPV4 remodels its surrounding plasmalemmal environment by manipulating cholesterol dynamics through Ca2+ influx.

Nano-clusters of ligand-activated integrins organize immobile, signalling active, nano-clusters of phosphorylated FAK required for mechanosignaling in focal adhesions

Transmembrane signalling receptors, such as integrins, organise as nanoclusters that are thought to provide several advantages including, increasing avidity, sensitivity (increasing the signal-to-noise ratio) and robustness (signalling above a threshold rather than activation by a single receptor) of the signal compared to signalling by single receptors. Compared to large micron-sized clusters, nanoclusters offer the advantage of rapid turnover for the disassembly of the signal. However, if nanoclusters function as signalling hubs remains poorly understood. Here, we employ fluorescence nanoscopy combined with photoactivation and photobleaching at sub-diffraction limited resolution of ~100nm length scale within a focal adhesion to examine the dynamics of diverse focal adhesion proteins. We show that (i) subregions of focal adhesions are enriched in immobile population of integrin β3 organised as nanoclusters, which (ii) in turn serve to organise nanoclusters of associated key adhesome proteins- vinculin, focal adhesion kinase (FAK) and paxillin, demonstrating that signalling proceeds by formation of nanoclusters rather than through individual proteins. (iii) Distinct focal adhesion protein nanoclusters exhibit distinct dynamics dependent on function. (iv) long-lived nanoclusters function as signalling hubs- wherein phosphorylated FAK and paxillin formed stable nanoclusters in close proximity to immobile integrin nanoclusters which are disassembled in response to inactivation signal by phosphatase PTPN12 (v) signalling takes place in response to an external signal such as force or geometric arrangement of the nanoclusters and when the signal is removed, these nanoclusters disassemble. Taken together, these results demonstrate that signalling downstream of transmembrane receptors is organised as hubs of signalling proteins (FAK, paxillin, vinculin) seeded by nanoclusters of the transmembrane receptor (integrin).

Distinct interactions stabilize EGFR dimers and higher-order oligomers in cell membranes

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase with important roles in many cellular processes as well as in cancer and other diseases. EGF binding promotes EGFR dimerization and autophosphorylation through interactions that are well understood structurally. How these dimers relate to higher-order EGFR oligomers seen in cell membranes, however, remains unclear. Here, we used single-particle tracking (SPT) and Förster resonance energy transfer imaging to examine how each domain of EGFR contributes to receptor oligomerization and the rate of receptor diffusion in the cell membrane. Although the extracellular region of EGFR is sufficient to drive receptor dimerization, we find that the EGF-induced EGFR slowdown seen by SPT requires higher-order oligomerization-mediated in part by the intracellular tyrosine kinase domain when it adopts an active conformation. Our data thus provide important insight into the interactions required for higher-order EGFR assemblies involved in EGF signaling.

Distinct interactions stabilize EGFR dimers and higher-order oligomers in cell membranes

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase (RTK) with important roles in many cellular processes as well as cancer and other diseases. EGF binding promotes EGFR dimerization and autophosphorylation through interactions that are well understood structurally. However, it is not clear how these dimers relate to higher-order EGFR oligomers detected at the cell surface. We used single-particle tracking (SPT) and Förster resonance energy transfer (FRET) imaging to examine how each domain within EGFR contributes to receptor dimerization and the rate of its diffusion in the cell membrane. We show that the EGFR extracellular region is sufficient to drive receptor dimerization, but that the EGF-induced EGFR slow-down seen by SPT requires formation of higher order oligomers, mediated in part by the intracellular tyrosine kinase domain - but only when in its active conformation. Our data thus provide important insight into higher-order EGFR interactions required for EGF signaling.

Field model for multistate lateral diffusion of various transmembrane proteins observed in living Dictyostelium cells

The lateral diffusion of transmembrane proteins on plasma membranes is a fundamental process for various cellular functions. Diffusion properties specific for individual protein species have been extensively studied, but the common features among protein species are poorly understood. Here, we systematically studied the lateral diffusion of various transmembrane proteins in the lower eukaryote Dictyostelium discoideum cells using a hidden Markov model for single-molecule trajectories obtained experimentally. As common features, all membrane proteins that had from one to ten transmembrane regions adopted three free diffusion states with similar diffusion coefficients regardless of their structural variability. All protein species reduced their mobility similarly upon the inhibition of microtubule or actin cytoskeleton dynamics, or myosin II. The relationship between protein size and the diffusion coefficient was consistent with the Saffman-Delbrück model, meaning that membrane viscosity is a major determinant of lateral diffusion, but protein size is not. These protein species-independent properties of multistate free diffusion were explained simply and quantitatively by free diffusion on the three membrane regions with different viscosities, which is in sharp contrast to the complex diffusion behavior of transmembrane proteins in higher eukaryotes.

Structure and dynamics of the EGFR/HER2 heterodimer

HER2 belongs to the human epidermal growth factor receptor tyrosine kinase family. Its overexpression or hyperactivation is a leading cause for multiple types of cancers. HER2 functions mainly through dimerization with other family members, such as EGFR. However, the molecular details for heterodimer assembly have not been completely understood. Here, we report cryo-EM structures of the EGF- and epiregulin-bound EGFR/HER2 ectodomain complexes at resolutions of 3.3 Å and 4.5 Å, respectively. Together with the functional analyses, we demonstrate that only the dimerization arm of HER2, but not that of EGFR, is essential for their heterodimer formation and signal transduction. Moreover, we analyze the differential membrane dynamics and transient interactions of endogenous EGFR and HER2 molecules in genome-edited cells using single-molecule live-cell imaging. Furthermore, we show that the interaction with HER2 could allow EGFR to resist endocytosis. Together, this work deepens our understanding of the unique structural properties and dynamics of the EGFR/HER2 complex.

Spatially Reprogramed Receptor Organization to Switch Cell Behavior Using a DNA Origami-Templated Aptamer Nanoarray

Receptor oligomerization is a highly complex molecular process that modulates divergent cell signaling. However, there is a lack of molecular tools for systematically interrogating how receptor oligomerization governs the signaling response. Here, we developed a DNA origami-templated aptamer nanoarray (DOTA) that enables precise programming of the oligomerization of receptor tyrosine kinases (RTK) with defined valency, distribution, and stoichiometry at the ligand-receptor interface. The DOTA allows for advanced receptor manipulations by arraying either monomeric aptamer ligands (mALs) that oligamerize receptor monomers to elicit artificial signaling or dimeric aptamer ligands (dALs) that preorganize the receptor dimer to recapitulate natural activation. We demonstrated that the multivalency and nanoscale spacing of receptor oligomerization coordinately influence the activation level of receptor tyrosine kinase signaling. Furthermore, we illustrated that DOTA-modulated receptor oligomerization could function as a signaling switch to promote the transition from epithelia to mesenchymal-like cells, demonstrating robust control over cellular behaviors. Together, we present a versatile all-in-one DNA nanoplatform for the systematical investigation and regulation of receptor-mediated cellular response.

Threonine phosphorylation regulates the molecular assembly and signaling of EGFR in cooperation with membrane lipids

The cytoplasmic domain of the receptor tyrosine kinases (RTKs) plays roles as a phosphorylation enzyme and a protein scaffold but the allocation of these two functions is not fully understood. We here analyzed assembly of the transmembrane (TM)-juxtamembrane (JM) region of EGFR, one of the best studied species of RTKs, by combining single-pair FRET imaging and a nanodisc technique. The JM domain of EGFR contains a threonine residue (Thr654) that is phosphorylated after ligand association. We observed that the TM-JM peptides of EGFR form anionic lipid-induced dimers and cholesterol-induced oligomers. The two forms involve distinct molecular interactions, with a bias towards oligomer formation upon threonine phosphorylation. We further analyzed the functions and oligomerization of whole EGFR molecules, with or without a substitution of Thr654 to alanine, in living cells. The results suggested an autoregulatory mechanism in which Thr654 phosphorylation causes a switch of the major function of EGFR from kinase activation dimers to scaffolding oligomers.

A two-component protein condensate of the EGFR cytoplasmic tail and Grb2 regulates Ras activation by SOS at the membrane

SignificanceTwo-dimensional condensates of proteins on the membrane surface, driven by tyrosine phosphorylation, are beginning to emerge as important players in signal transduction. This work describes discovery of a protein condensation phase transition of EGFR and Grb2 on membrane surfaces, which is poised to have a significant impact on how we understand EGFR signaling and misregulation in disease. EGFR condensation is mediated through a Grb2-Grb2 crosslinking element, which itself is regulatable through a specific phosphotyrosine site on Grb2. Furthermore, the EGFR condensate exerts significant control over the ability of SOS to activate Ras, thus implicating the EGFR condensate as a regulator of signal propagation from EGFR to Ras and the MAPK pathway.

Triple-color single-molecule imaging for analysis of the role of receptor oligomers in signal transduction

Membrane receptors provide interfaces of various extracellular stimuli to transduce the signal into the cell. Receptors are required to possess such conflicting properties as high sensitivity and noise reduction for the cell to keep its homeostasis and appropriate responses. To understand the mechanisms by which these functions are achieved, single-molecule monitoring of the motilities of receptors and signaling molecules on the plasma membrane is one of the most direct approaches. This review article introduces several recent single-molecule imaging studies of receptors, including the author’s recent work on triple-color single-molecule imaging of G protein-coupled receptors. Based on these researches, advantages and perspectives of the single-molecule imaging approach to solving the mechanisms of receptor functions are illustrated.

Live-Cell Imaging of Single Neurotrophin Receptor Molecules on Human Neurons in Alzheimer's Disease

Neurotrophin receptors such as the tropomyosin receptor kinase A receptor (TrkA) and the low-affinity binding p75 neurotrophin receptor p75^NTR play a critical role in neuronal survival and their functions are altered in Alzheimer’s disease (AD). Changes in the dynamics of receptors on the plasma membrane are essential to receptor function. However, whether receptor dynamics are affected in different pathophysiological conditions is unexplored. Using live-cell single-molecule imaging, we examined the surface trafficking of TrkA and p75^NTR molecules on live neurons that were derived from human-induced pluripotent stem cells (hiPSCs) of presenilin 1 (PSEN1) mutant familial AD (fAD) patients and non-demented control subjects. Our results show that the surface movement of TrkA and p75^NTR and the activation of TrkA- and p75^NTR-related phosphoinositide-3-kinase (PI3K)/serine/threonine-protein kinase (AKT) signaling pathways are altered in neurons that are derived from patients suffering from fAD compared to controls. These results provide evidence for altered surface movement of receptors in AD and highlight the importance of investigating receptor dynamics in disease conditions. Uncovering these mechanisms might enable novel therapies for AD.

Heterogeneity in VEGF Receptor-2 Mobility and Organization on the Endothelial Cell Surface Leads to Diverse Models of Activation by VEGF

The dynamic nanoscale organization of cell surface receptors plays an important role in signaling. We determine this organization and its relation to activation of VEGF receptor-2 (VEGFR-2), a critical receptor tyrosine kinase in endothelial cells (ECs), by combining single-molecule imaging of endogenous VEGFR-2 in live ECs with multiscale computational analysis. We find that surface VEGFR-2 can be mobile or exhibit restricted mobility and be monomeric or non-monomeric, with a complex interplay between the two. This basal heterogeneity results in heterogeneity in the sequence of steps leading to VEGFR-2 activation by VEGF. Specifically, we find that VEGF can bind to monomeric and non-monomeric VEGFR-2 and that, when binding to monomeric VEGFR-2, its effect on dimerization depends on the mobility of VEGFR-2. Our study highlights the dynamic and heterogeneous nature of cell surface receptor organization and the need for multiscale, single-molecule-based analysis to determine its relationship to receptor activation and signaling.

da Rocha-Azevedo et al. show that VEGFR-2 exhibits mobility and interaction heterogeneity on the endothelial cell surface. The sequence of steps leading to VEGFR-2 activation by VEGF depends on the basal state of VEGFR-2. Thus, there is not one model but multiple co-existing models of VEGFR-2 activation by VEGF.

Comparative Analysis of Single-Molecule Dynamics of TRPV1 and TRPV4 Channels in Living Cells

TRPV1 and TRPV4, members of the transient receptor potential vanilloid family, are multimodal ion channels activated by various stimuli, including temperature and chemicals. It has been demonstrated that TRPV channels function as tetramers; however, the dynamics of the diffusion, oligomerization, and endocytosis of these channels in living cells are unclear. Here we undertook single-molecule time-lapse imaging of TRPV1 and TRPV4 in HEK 293 cells. Differences were observed between TRPV1 and TRPV4 before and after agonist stimulation. In the resting state, TRPV4 was more likely to form higher-order oligomers within immobile membrane domains than TRPV1. TRPV1 became immobile after capsaicin stimulation, followed by its gradual endocytosis. In contrast, TRPV4 was rapidly internalized upon stimulation with GSK1016790A. The selective loss of immobile higher-order oligomers from the cell surface through endocytosis increased the proportion of the fast-diffusing state for both subtypes. With the increase in the fast state, the association rate constants of TRPV1 and TRPV4 increased, regenerating the higher-order oligomers. Our results provide a possible mechanism for the different rates of endocytosis of TRPV1 and TRPV4 based on the spatial organization of the higher-order structures of the two TRPV channels.

p52Shc regulates the sustainability of ERK activation in a RAF-independent manner

p52SHC (SHC) and GRB2 are adaptor proteins involved in the RAS/MAPK (ERK) pathway mediating signals from cell-surface receptors to various cytoplasmic proteins. To further examine their roles in signal transduction, we studied the translocation of fluorescently labeled SHC and GRB2 to the cell surface, caused by the activation of ERBB receptors by heregulin (HRG). We simultaneously evaluated activated ERK translocation to the nucleus. Unexpectedly, the translocation dynamics of SHC were sustained when those of GRB2 were transient. The sustained localization of SHC positively correlated with the sustained nuclear localization of ERK, which became more transient after SHC knockdown. SHC-mediated PI3K activation was required to maintain the sustainability of the ERK translocation regulating MEK but not RAF. In cells overexpressing ERBB1, SHC translocation became transient, and the HRG-induced cell fate shifted from a differentiation to a proliferation bias. Our results indicate that SHC and GRB2 functions are not redundant but that SHC plays the critical role in the temporal regulation of ERK activation.

In-Cell Single-Molecule Analysis of Molecular State and Reaction Kinetics Coupling

Cellular signaling is regulated by the spatiotemporal dynamics and kinetics of molecular behavior. To investigate the mechanisms at the molecular level, fluorescence single-molecule analysis is an effective method owing to the direct observation of individual molecules in situ in cells and the results in quantitative information about the behavior. The integration of machine learning into this analysis modality enables the acquisition of behavioral features at all time points of all molecules. As a case study, we described a hidden Markov model-based approach to infer the molecular states of mobility and clustering for epidermal growth factor receptor (EGFR) along a single-molecule trajectory. We reveal a scheme of the receptor signaling through the dynamic coupling of the mobility and clustering states under the influence of a local membrane structure. As the activation process progressed, EGFR generally converged to an immobile cluster. This state exhibited high affinity with a specific cytoplasmic protein, shown by two-color single-molecule analysis, and could be a platform for downstream signaling. The method was effective for elucidating the biophysical mechanisms of signaling regulation when comprehensive analysis is possible for a huge number and multiple molecular species in the signaling pathway. Thus, a fully automated system for single-molecule analysis, in which indispensable expertise was replicated using artificial intelligence, has been developed to enable in-cell large-scale analysis. This system opens new single-molecule approaches for pharmacological applications as well as the basic sciences.

Workflows of the Single-Molecule Imaging Analysis in Living Cells: Tutorial Guidance to the Measurement of the Drug Effects on a GPCR

Single-molecule imaging (SMI) is a powerful method to measure the dynamics of membrane proteins on the cell membrane. The single-molecule tracking (SMT) analysis provides information about the diffusion dynamics, the oligomer size distribution, and the particle density change. The affinity and on/off-rate of a protein-protein interaction can be estimated from the dual-color SMI analysis. However, it is difficult for trainees to determine quantitative information from the SMI movies. The present protocol guides the detailed workflows to measure the drug-activated dynamics of a G protein-coupled receptor (GPCR) and metabotropic glutamate receptor 3 (mGluR3), by using the total internal reflection fluorescence microscopy (TIRFM). This tutorial guidance comprises an open-source software, named smDynamicsAnalyzer, with which one can easily analyze the SMT dataset by just following the workflows after building a designated folder structure ( https://github.com/masataka-yanagawa/IgorPro8-smDynamicsAnalyzer ).

A DNA-nanoassembly-based approach to map membrane protein nanoenvironments

Most proteins at the plasma membrane are not uniformly distributed but localize to dynamic domains of nanoscale dimensions. To investigate their functional relevance, there is a need for methods that enable comprehensive analysis of the compositions and spatial organizations of membrane protein nanodomains in cell populations. Here we describe the development of a non-microscopy-based method for ensemble analysis of membrane protein nanodomains. The method, termed nanoscale deciphering of membrane protein nanodomains (NanoDeep), is based on the use of DNA nanoassemblies to translate membrane protein organization information into a DNA sequencing readout. Using NanoDeep, we characterized the nanoenvironments of Her2, a membrane receptor of critical relevance in cancer. Importantly, we were able to modulate by design the inventory of proteins analysed by NanoDeep. NanoDeep has the potential to provide new insights into the roles of the composition and spatial organization of protein nanoenvironments in the regulation of membrane protein function.

Signaling activations through G-protein-coupled-receptor aggregations

Eukaryotic cells transmit extracellular signal information to cellular interiors through the formation of a ternary complex made up of a ligand (or agonist), G-protein, and G-protein-coupled receptor (GPCR). Previously formalized theories of ternary complex formation have mainly assumed that observable states of receptors can only take the form of monomers. Here, we propose a multiary complex model of GPCR signaling activations via the vector representation of various unobserved aggregated receptor states. Our results from model simulations imply that receptor aggregation processes can govern cooperative effects in a regime inaccessible by previous theories. In particular, we show how the affinity of ligand-receptor binding can be largely varied by various oligomer formations in the low concentration range of G-protein stimulus.

Large-scale single-molecule imaging aided by artificial intelligence

Single-molecule imaging analysis has been applied to study the dynamics and kinetics of molecular behaviors and interactions in living cells. In spite of its high potential as a technique to investigate the molecular mechanisms of cellular phenomena, single-molecule imaging analysis has not been extended to a large scale of molecules in cells due to the low measurement throughput as well as required expertise. To overcome these problems, we have automated the imaging processes by using computer operations, robotics and artificial intelligence (AI). AI is an ideal substitute for expertise to obtain high-quality images for quantitative analysis. Our automated in-cell single-molecule imaging system, AiSIS, could analyze 1600 cells in 1 day, which corresponds to ∼ 100-fold higher efficiency than manual analysis. The large-scale analysis revealed cell-to-cell heterogeneity in the molecular behavior, which had not been recognized in previous studies. An analysis of the receptor behavior and downstream signaling was accomplished within a significantly reduced time frame and revealed the detailed activation scheme of signal transduction, advancing cell biology research. Furthermore, by combining the high-throughput analysis with our previous finding that a receptor changes its behavioral dynamics depending on the presence of a ligand/agonist or inhibitor/antagonist, we show that AiSIS is applicable to comprehensive pharmacological analysis such as drug screening. This AI-aided automation has wide applications for single-molecule analysis.

In-cell structural dynamics of an EGF receptor during ligand-induced dimer-oligomer transition

The epidermal growth factor receptor (EGFR) is a membrane protein that regulates cell proliferation, differentiation and survival, and is a drug target for cancer therapy. Ligand-induced activation of the EGFR kinase is generally regarded to require ligand-bound-dimers, while phosphorylation and down-stream signalling is modulated by oligomers. Recent work has unveiled changes in EGFR dynamics from ligand-induced dimerization in membranes extracted from cells, however, less is known about the changes in EGFR dynamics that accompany the ligand-induced oligomerization in a live cell environment. Here, we determine the dynamics of a c-terminal GFP tag attached to EGFR in the unliganded dimer and in the liganded oligomers. By means of the single-frequency polarized phasor ellipse approach we extracted two correlation times on the sub-nanosecond and super-nanosecond timescales, respectively. EGF binding to the EGFR-GFP dimer lengthened the sub-nanosecond correlation time (from 0.1 to 1.3 ns) and shortened the super-nanosecond correlation time (from 210 to 56 ns) of the c-terminal GFP probe. The sub-nanosecond depolarization processes were assigned to electronic energy migration between proximal GFPs in the EGFR dimer or oligomer, while the super-nanosecond correlation times were assigned to nanosecond fluctuations of the GFP probe in the EGFR complex. Accordingly, these results show that ligand binding increased the average separation between the c-terminal tags and increased their rotational mobility. We propose that the dynamics are linked to an inhibitory function of the c-terminal tail in the un-liganded dimer and to the requirement of facile stochastic switching between kinase activation and cytoplasmic adaptor/effector binding in the active oligomers.

Resolvin E3 attenuates allergic airway inflammation via the interleukin-23-interleukin-17A pathway

We investigated the effects of resolvin E (RvE) 1, RvE2, and RvE3 on IL-4- and IL-33-stimulated bone marrow-derived dendritic cells (BMDCs) from house dust mite (HDM)-sensitized mice. We also investigated the role of RvE3 in a murine model of HDM-induced airway inflammation. In vitro, BMDCs from HDM-sensitized mice were stimulated with IL-4 and IL-33 and then treated with RvE1, RvE2, RvE3, or vehicle. RvE1, RvE2, and RvE3 suppressed IL-23 release from BMDCs. In vivo, RvE3 administrated to HDM-sensitized and challenged mice in the resolution phase promoted a decline in total numbers of inflammatory cells and eosinophils, reduced levels of IL-23 and IL-17 in lavage fluid, and suppressed IL-23 and IL-17A mRNA expression in lung and peribronchial lymph nodes. RvE3 also reduced resistance in the lungs of HDM-sensitized mice. A NanoBiT β-arrestin recruitment assay using human embryonic kidney 293 cells revealed that pretreatment with RvE3 suppressed the leukotriene B4 (LTB4)-induced β-arrestin 2 binding to LTB4 receptor 1 (BLT1R), indicating that RvE3 antagonistically interacts with BLT1R. Collectively, these findings indicate that RvE3 facilitates the resolution of allergic airway inflammation, partly by regulating BLT1R activity and selective cytokine release by dendritic cells. Our results accordingly identify RvE3 as a potential therapeutic target for the management of asthma.-Sato, M., Aoki-Saito, H., Fukuda, H., Ikeda, H., Koga, Y., Yatomi, M., Tsurumaki, H., Maeno, T., Saito, T., Nakakura, T., Mori, T., Yanagawa, M., Abe, M., Sako, Y., Dobashi, K., Ishizuka, T., Yamada, M., Shuto, S., Hisada, T. Resolvin E3 attenuates allergic airway inflammation via the interleukin-23-interleukin-17A pathway.

A Brief History of Single-Particle Tracking of the Epidermal Growth Factor Receptor

Single-particle tracking (SPT) has been used and developed over the last 25 years as a method to investigate molecular dynamics, structure, interactions, and function in the cellular context. SPT is able to show how fast and how far individual molecules move, identify different dynamic populations, measure the duration and strength of intermolecular interactions, and map out structures on the nanoscale in cells. In combination with other techniques such as macromolecular crystallography and molecular dynamics simulation, it allows us to build models of complex structures, and develop and test hypotheses of how these complexes perform their biological roles in health as well as in disease states. Here, we use the example of the epidermal growth factor receptor (EGFR), which has been studied extensively by SPT, demonstrating how the method has been used to increase our understanding of the receptor’s organization and function, including its interaction with the plasma membrane, its activation, clustering, and oligomerization, and the role of other receptors and endocytosis. The examples shown demonstrate how SPT might be employed in the investigation of other biomolecules and systems.

Single-Molecule Förster Resonance Energy Transfer Measurement Reveals the Dynamic Partially Ordered Structure of the Epidermal Growth Factor Receptor C-Tail Domain

Intrinsically disordered proteins (IDPs) or regions (IDRs) are thought to exhibit unique functionalities without forming ordered structures. However, these molecular mechanisms are not easily elucidated, partly because of the difficultly of measuring structural information. In this study, we applied the alternative laser excitation (ALEX) method and circular dichroism (CD) spectroscopy to investigate the structure of the C-terminal tail (CTT) domain of the human epidermal growth factor receptor (EGFR). The single-molecule distributions of Förster resonance energy transfer (FRET) obtained by ALEX under solution conditions modified by the addition of potassium chloride (KCl), urea, or guanidinium chloride (GdmCl) allowed us to separately examine the influences of charge interactions and secondary structure formation. The CD spectrum analyses indicated the types of included secondary structure. The results suggested that the structure of the CTT is influenced by secondary structure formation, which is a principally antiparallel β-sheet, rather than by charge interactions and that phosphorylation of the major Grb2-binding sites partially denatures that secondary structure. Our findings suggest that the EGFR CTT might regulate ligand binding kinetics by local β-sheet formation or by the disruption associated with phosphorylation states.

Who's In and Who's Out-Compositional Control of Biomolecular Condensates

Biomolecular condensates are two- and three-dimensional compartments in eukaryotic cells that concentrate specific collections of molecules without an encapsulating membrane. Many condensates behave as dynamic liquids and appear to form through liquid-liquid phase separation driven by weak, multivalent interactions between macromolecules. In this review, we discuss current models and data regarding the control of condensate composition, and we describe our current understanding of the composition of representative condensates including PML nuclear bodies, P-bodies, stress granules, the nucleolus, and two-dimensional membrane localized LAT and nephrin clusters. Specific interactions, such as interactions between modular binding domains, weaker interactions between intrinsically disorder regions and nucleic acid base pairing, and nonspecific interactions, such as electrostatic interactions and hydrophobic interactions, influence condensate composition. Understanding how specific condensate composition is determined is essential to understanding condensates as biochemical entities and ultimately discerning their cellular and organismic functions.

Automated single-molecule imaging in living cells

An automated single-molecule imaging system developed for live-cell analyses based on artificial intelligence-assisted microscopy is presented. All significant procedures, i.e., searching for cells suitable for observation, detecting in-focus positions, and performing image acquisition and single-molecule tracking, are fully automated, and numerous highly accurate, efficient, and reproducible single-molecule imaging experiments in living cells can be performed. Here, the apparatus is applied for single-molecule imaging and analysis of epidermal growth factor receptors (EGFRs) in 1600 cells in a 96-well plate within 1 day. Changes in the lateral mobility of EGFRs on the plasma membrane in response to various ligands and drug concentrations are clearly detected in individual cells, and several dynamic and pharmacological parameters are determined, including the diffusion coefficient, oligomer size, and half-maximal effective concentration (EC50). Automated single-molecule imaging for systematic cell signaling analyses is feasible and can be applied to single-molecule screening, thus extensively contributing to biological and pharmacological research.