Jasplakinolide: an actin-specific reagent that promotes actin polymerization

Optimizing Jasplakinolide delivery in rhabdomyosarcoma cells using pulsed electric fields (PEFs) for enhanced therapeutic impact

This study explores the combination of jasplakinolide with electroporation (JSP + EP), a method enhancing targeted molecule delivery. CHO-K1 (Chinese hamster ovarian), C2C12 (mouse myoblast), and RD (rhabdomyosarcoma) cells were treated with jasplakinolide (50 nM) in HEPES buffer and exposed to electrical pulses (0.8-1.2 kV/cm). Cell viability was measured via the MTS assay, cytoskeleton structure was assessed with confocal microscopy, and docking studies examined jasplakinolide-actin interactions. The combination of jasplakinolide and electric pulses synergistically affected RMS cells (Rhabdomyosarcoma), causing significant cytoskeletal changes and reduced viability. Docking studies revealed that jasplakinolide interacts with both monomeric and filamentous actin, highlighting a dual mechanism. Confocal imaging showed substantial actin cytoskeleton disruption in cancer cells, with minimal effects on normal cells. Jasplakinolide combined with electric pulses can specifically target cancer cells with less cytotoxicity to normal cells, potentially reducing side effects following the clinical procedure.

Receptor polarization through localized activity and global sensitization

Eukaryotic cells chemosense concentration gradients of extracellular ligands using membrane-bound receptors that polarize their activity. Receptors from several chemosensing families are preferentially degraded after activation and undergo significant lateral diffusion, both of which may blunt their polarization. To explore the combined role of these two seemingly detrimental phenomena on active receptor polarization, we use a reaction/diffusion model. The model elucidates a counterintuitive principle that governs receptor polarization under external gradients: Localized Activity and Global Sensitization (LAGS). In LAGS, receptor activity is localized through receptor degradation or ligand unbinding. In contrast, uniform sensitivity to ligands is maintained over the plasma membrane through lateral receptor diffusion. Surprisingly, increasing preferential degradation of active receptors and increasing lateral diffusion of all receptors both sharpen active receptor polarization. Additionally, when combined with receptor oligomerization, an increase in preferential degradation allows cells to sense relative ligand gradients over a larger range of background ligand concentrations. An analytical model identifies parameter regimes that dictate which processes dominate receptor polarization. A survey of kinetic parameters suggests that receptor polarization in many mammalian pathways can be modeled using LAGS.

The application of explants, crypts, and organoids as models in intestinal barrier research

In vitro models are of great importance in advancing our understanding of human diseases, especially complex disorders with unknown etiologies like inflammatory bowel diseases (IBD). One of the key IBD features is the increased intestinal permeability. The disruption of the intestinal barrier can occur due to a destructive inflammatory response involving intestinal cell death. Alternatively, proteins that form tight junctions (TJ) fail to form function complexes and promote epithelial barrier disruption. The mechanisms behind this process are not fully understood. Thus, in vitro models that facilitate studying the intestinal barrier and its molecular components are of particular importance in the context of IBD. There are in vitro and ex vivo models that can be used to recapitulate some aspects of IBD. Among these are intestinal explants, crypts, and epithelial 3D-organoids. Here we describe some practical limitations of isolated crypts, gut tissue explants, and intestinal organoids as models in epithelial barrier biology, and TJ in particular. Our findings demonstrate that only 3D intestinal organoids formed from single cells are suitable to study barrier permeability in vitro, as primary crypt-derived organoids do not retain epithelial integrity due to cell death. Importantly, 3D organoids raised in culture conditions may fail to recapitulate inflammatory and barrier phenotypes of the source mouse model. To study the features of the inflamed epithelium, ex vivo intestinal explants and crypts were employed. We show here that isolated crypts do not preserve native TJ structure in a long-term experimental setting and tend to disintegrate in the unsupported culture environment. However, intestinal explants were stable in culture conditions for about 24 hours and demonstrated their applicability for short-term living tissue imaging and fluorescence recovery after photobleaching (FRAP). Thus, a combination of 3D organoids and intestinal explants provides a more accurate experimental platform to understand the intestinal epithelial barrier.

CK-666 protects against ferroptosis and renal ischemia-reperfusion injury through a microfilament-independent mechanism

Ferroptosis is a type of regulated cell death driven by iron-dependent accumulation of lipid peroxidation, exhibiting unique morphological changes. While actin microfilaments are crucial for various cellular processes, including morphogenesis, motility, endocytosis, and cell death, their role in ferroptosis remains unclear. Here, our study reveals that actin microfilaments undergo remodeling and disassembly during ferroptosis. Interestingly, inhibitors that target actin microfilament remodeling do not affect cell sensitivity to ferroptosis, with the exception of CK-666 and its structural analog CK-636. Mechanistically, CK-666 attenuates ferroptosis independently of its canonical function in inhibiting the Arp2/3 complex. Further investigation revealed that CK-666 modulates the ferroptotic transcriptome, prevents lipid degradation, and diminishes lipid peroxidation. In addition, CK-666 does not impact the labile iron pool within cells nor does the inhibition of FSP1 impacts its antiferroptosis activity. Notably, the results of DPPH assay and liposome leakage assay suggest that CK-666 mitigates ferroptosis by directly eliminating lipid peroxidation. Importantly, CK-666 significantly ameliorated renal ischemia-reperfusion injury and ferroptosis in renal tissue, underscoring its potential therapeutic impact.

Microscale geometrical modulation of PIEZO1 mediated mechanosensing through cytoskeletal redistribution

The microgeometry of the cellular microenvironment profoundly impacts cellular behaviors, yet the link between it and the ubiquitously expressed mechanosensitive ion channel PIEZO1 remains unclear. Herein, we describe a fluorescent micropipette aspiration assay that allows for simultaneous visualization of intracellular calcium dynamics and cytoskeletal architecture in real-time, under varied micropipette geometries. By integrating elastic shell finite element analysis with fluorescent lifetime imaging microscopy and employing PIEZO1-specific transgenic red blood cells and HEK cell lines, we demonstrate a direct correlation between the microscale geometry of aspiration and PIEZO1-mediated calcium signaling. We reveal that increased micropipette tip angles and physical constrictions lead to a significant reorganization of F-actin, accumulation at the aspirated cell neck, and subsequently amplify the tension stress at the dome of the cell to induce more PIEZO1's activity. Disruption of the F-actin network or inhibition of its mobility leads to a notable decline in PIEZO1 mediated calcium influx, underscoring its critical role in cellular mechanosensing amidst geometrical constraints.

The actin-binding protein CAP1 represses MRTF-SRF-dependent gene expression in mouse cerebral cortex

Serum response factor (SRF) is an essential transcription factor for brain development and function. Here, we explored how an SRF cofactor, the actin monomer-sensing myocardin-related transcription factor MRTF, is regulated in mouse cortical neurons. We found that MRTF-dependent SRF activity in vitro and in vivo was repressed by cyclase-associated protein CAP1. Inactivation of the actin-binding protein CAP1 reduced the amount of actin monomers in the cytoplasm, which promoted nuclear MRTF translocation and MRTF-SRF activation. This function was independent of cofilin1 and actin-depolymerizing factor, and CAP1 loss of function in cortical neurons was not compensated by endogenous CAP2. Transcriptomic and proteomic analyses of cerebral cortex lysates from wild-type and Cap1 knockout mice supported the role of CAP1 in repressing MRTF-SRF-dependent signaling in vivo. Bioinformatic analysis identified likely MRTF-SRF target genes, which aligned with the transcriptomic and proteomic results. Together with our previous studies that implicated CAP1 in axonal growth cone function as well as the morphology and plasticity of excitatory synapses, our findings establish CAP1 as a crucial actin regulator in the brain relevant for formation of neuronal networks.

Cell softness renders cytotoxic T lymphocytes and T leukemic cells resistant to perforin-mediated killing

Mechanical force contributes to perforin pore formation at immune synapses, thus facilitating the cytotoxic T lymphocytes (CTL)-mediated killing of tumor cells in a unidirectional fashion. How such mechanical cues affect CTL evasion of perforin-mediated autolysis remains unclear. Here we show that activated CTLs use their softness to evade perforin-mediated autolysis, which, however, is shared by T leukemic cells to evade CTL killing. Downregulation of filamin A is identified to induce softness via ZAP70-mediated YAP Y357 phosphorylation and activation. Despite the requirements of YAP in both cell types for softness induction, CTLs are more resistant to YAP inhibitors than malignant T cells, potentially due to the higher expression of the drug-resistant transporter, MDR1, in CTLs. As a result, moderate inhibition of YAP stiffens malignant T cells but spares CTLs, thus allowing CTLs to cytolyze malignant cells without autolysis. Our findings thus hint a mechanical force-based immunotherapeutic strategy against T cell leukemia.

Therapeutic Potential of Marine-Derived Cyclic Peptides as Antiparasitic Agents

Parasitic diseases still compromise human health. Some of the currently available therapeutic drugs have limitations considering their adverse effects, questionable efficacy, and long treatment, which have encouraged drug resistance. There is an urgent need to find new, safe, effective, and affordable antiparasitic drugs. Marine-derived cyclic peptides have been increasingly screened as candidates for developing new drugs. Therefore, in this review, a systematic analysis of the scientific literature was performed and 25 marine-derived cyclic peptides with antiparasitic activity (1-25) were found. Antimalarial activity is the most reported (51%), followed by antileishmanial (27%) and antitrypanosomal (20%) activities. Some compounds showed promising antiparasitic activity at the nM scale, being active against various parasites. The mechanisms of action and targets for some of the compounds have been investigated, revealing different strategies against parasites.

HIV-1 diverts cortical actin for particle assembly and release

Enveloped viruses assemble and bud from the host cell membranes. Any role of cortical actin in these processes have often been a source of debate. Here, we assessed if cortical actin was involved in HIV-1 assembly in infected CD4 T lymphocytes. Our results show that preventing actin branching not only increases HIV-1 particle release but also the number of individual HIV-1 Gag assembly clusters at the T cell plasma membrane. Indeed, in infected T lymphocytes and in in vitro quantitative model systems, we show that HIV-1 Gag protein prefers areas deficient in F-actin for assembling. Finally, we found that the host factor Arpin, an inhibitor of Arp2/3 branched actin, is recruited at the membrane of infected T cells and it can associate with the viral Gag protein. Altogether, our data show that, for virus assembly and particle release, HIV-1 prefers low density of cortical actin and may favor local actin debranching by subverting Arpin.

Actin polymerization inhibition by targeting ARPC2 affects intestinal stem cell homeostasis

Background

The rapid turnover of the intestinal epithelium is driven by the proliferation and differentiation of intestinal stem cells (ISCs). The dynamics of the F-actin cytoskeleton are critical for maintaining intercellular force and the signal transduction network. However, it remains unclear how direct interference with actin polymerization impacts ISC homeostasis. This study aims to reveal the regulatory effects of the F-actin cytoskeleton on the homeostasis of intestinal epithelium, as well as the potential risks of benproperine (BPP) as an anti-tumor drug.

Methods

Phalloidin fluorescence staining was utilized to test F-actin polymerization. Flow cytometry and IHC staining were employed to discriminate different types of intestinal epithelial cells. Cell proliferation was assessed through bromo-deoxyuridine (BrdU) and 5-ethynyl-2'-deoxyuridine (EdU) incorporation assays. The proliferation and differentiation of intestinal stem cells were replicated in vitro through organoid culture. Epithelial migration was evaluated through BrdU pulse labeling and chasing in mice.

Results

The F-actin content was observed to significantly increase as crypt cells migrated into the villus region. Additionally, actin polymerization in secretory cells, especially in Paneth cells (PCs), was much higher than that in neighboring ISCs. Treatment with the newly identified actin-related protein 2/3 complex subunit 2 (ARPC2) inhibitor BPP led to a dose-dependent increase or inhibition of intestinal organoid growth in vitro and crypt cell proliferation in vivo. Compared with the vehicle group, BPP treatment decreased the expression of Lgr5 ISC feature genes in vivo and in organoid culture. Meanwhile, PC differentiation derived from ISCs and progenitors was decreased by inhibition of F-actin polymerization. Mechanistically, BPP-induced actin polymerization inhibition may activate the Yes1-associated transcriptional regulator pathway, which affects ISC proliferation and differentiation. Accordingly, BPP treatment affected intestinal epithelial cell migration in a dose-dependent manner.

Conclusion

Our findings indicate that the regulation of cytoskeleton reorganization can affect ISC homeostasis. In addition, inhibiting ARPC2 with the Food and Drug Administration-approved drug BPP represents a novel approach to influencing the turnover of intestinal epithelial cells.

Adseverin, an actin-binding protein, modulates hypertrophic chondrocyte differentiation and osteoarthritis progression

In osteoarthritis (OA), a disease characterized by progressive articular cartilage degradation and calcification, the articular chondrocyte phenotype changes and this correlates with actin cytoskeleton alterations suggesting that it regulates gene expression essential for proper phenotype. This study reports that OA is associated with the loss of adseverin, an actin capping and severing protein. Adseverin deletion (Adseverin-/-) in mice compromised articular chondrocyte function, by reducing F-actin and aggrecan expression and increasing apoptosis, Indian hedgehog, Runx2, MMP13, and collagen type X expression, and cell proliferation. This led to stiffer cartilage and decreased hyaline and increased calcified cartilage thickness. Together, these changes predisposed the articular cartilage to enhanced OA severity in Adseverin-/- mice who underwent surgical induction of OA. Adseverin-/- chondrocyte RNA sequencing and in vitro studies together suggests that adseverin modulates cell viability and prevents mineralization. Thus, adseverin maintains articular chondrocyte phenotype and cartilage tissue homeostasis by preventing progression to hypertrophic differentiation in vivo. Adseverin may be chondroprotective and a potential therapeutic target.

The influence of dysfunctional actin on polystyrene-nanotube-mediated mRNA nanoinjection into mammalian cells

The advancement of nanofabrication technologies has transformed the landscape of engineered nano-bio interfaces, especially with vertically aligned nanoneedles (NNs). This enables scientists to venture into new territories, widening NN applications into increasingly more complex cellular manipulation and interrogation. Specifically, for intracellular delivery application, NNs have been shown to mediate the delivery of various bioactive cargos into a wide range of cells-a physical method termed "nanoinjection". Silicon (Si) nanostructures demonstrated great potential in nanoinjection, whereas the use of polymeric NNs for nanoinjection has rarely been explored. Furthermore, the underlying mechanism of interaction at the cell-NN interface is subtle and multifaceted, and not fully understood-underpinned by the design versatility of the NN biointerface. Recent studies have suggested that actin dynamic plays a pivotal role influencing the delivery efficacy. In this study, we fabricated a new class of NNs-a programmable polymeric nanotubes (NTs)-from polystyrene (PS) cell cultureware, designed to facilitate mRNA delivery into mouse embryonic fibroblast GPE86 cells. The PSNT delivery platform was able to mediate mRNA delivery with high delivery efficiency (∼83%). We also investigated the role of actin cytoskeleton in PSNTs mediated intracellular delivery by introducing two actin inhibitors-cytochalasin D (Cyto D) and jasplakinolide (Jas)-to cause dysfunctional cytoskeleton, via inhibiting actin polymerization and depolymerization, respectively (before and after the establishment of cell-PSNT interface). By inhibiting actin dynamics 12 h before cell-PSNT interfacing (pre-interface treatment), the mRNA delivery efficiencies were significantly reduced to ∼3% for Cyto D-treated samples and ∼1% for Jas-treated sample, as compared to their post-interface (2 h after cell-PSNT interfacing) counterpart (∼46% and ∼68%, respectively). The added flexibility of PSNTs have shown to help withstand mechanical breakage stemming from cytoskeletal forces in contrast to the SiNTs. Such findings will step-change our capacity to use programmable polymeric NTs in fundamental cellular processes related to intracellular delivery.

Differential Control of Small-conductance Calcium-activated Potassium Channel Diffusion by Actin in Different Neuronal Subcompartments

Small-conductance calcium-activated potassium (SK) channels show a ubiquitous distribution on neurons, in both somatodendritic and axonal regions. SK channels are associated with neuronal activity regulating action potential frequency, dendritic excitability, and synaptic plasticity. Although the physiology of SK channels and the mechanisms that control their surface expression levels have been investigated extensively, little is known about what controls SK channel diffusion in the neuronal plasma membrane. This aspect is important, as the diffusion of SK channels at the surface may control their localization and proximity to calcium channels, hence increasing the likelihood of SK channel activation by calcium. In this study, we successfully investigated the diffusion of SK channels labeled with quantum dots on human embryonic kidney cells and dissociated hippocampal neurons by combining a single-particle tracking method with total internal reflection fluorescence microscopy. We observed that actin filaments interfere with SK mobility, decreasing their diffusion coefficient. We also found that during neuronal maturation, SK channel diffusion was gradually inhibited in somatodendritic compartments. Importantly, we observed that axon barriers formed at approximately days in vitro 6 and restricted the diffusion of SK channels on the axon initial segment (AIS). However, after neuron maturation, SK channels on the AIS were strongly immobilized, even after disruption of the actin network, suggesting that crowding may cause this effect. Altogether, our work provides insight into how SK channels diffuse on the neuronal plasma membrane and how actin and membrane crowding impacts SK channel diffusion.

Presynaptic Plasticity Is Associated with Actin Polymerization

Modulation of presynaptic short-term plasticity induced by actin polymerization was studied in rat hippocampal slices using the paired-pulse paradigm. Schaffer collaterals were stimulated with paired pulses with a 70-ms interstimulus interval every 30 s before and during perfusion with jasplakinolide, an activator of actin polymerization. Jasplakinolide application resulted in the increase in the amplitudes of CA3-CA1 responses (potentiation) accompanied by a decrease in the paired-pulse facilitation, suggesting induction of presynaptic modifications. Jasplakinolide-induced potentiation depended on the initial paired-pulse rate. These data indicate that the jasplakinolide-mediated changes in actin polymerization increased the probability of neurotransmitter release. Less typical for CA3-CA1 synapses responses, such as a very low paired-pulse ratio (close to 1 or even lower) or even paired-pulse depression, were affected differently. Thus, jasplakinolide caused potentiation of the second, but not the first response to the paired stimulus, which increased the paired-pulse ratio from 0.8 to 1.0 on average, suggesting a negative impact of jasplakinolide on the mechanisms promoting paired-pulse depression. In general, actin polymerization facilitated potentiation, although the patterns of potentiation differed depending on the initial synapse characteristics. We conclude that in addition to the increase in the neurotransmitter release probability, jasplakinolide induced other actin polymerization-dependent mechanisms, including those involved in the paired-pulse depression.

Adverse PFAS effects on mouse oocyte in vitro maturation are associated with carbon-chain length and inclusion of a sulfonate group

OBJECTIVES

Per- and polyfluoroalkyl substances (PFAS) are man-made chemicals that are widely used in various products. PFAS are characterized by their fluorinated carbon chains that make them hard to degrade and bioaccumulate in human and animals. Toxicological studies have shown PFAS toxic effects: cytotoxicity, immunotoxicity, neurotoxicity, and reproductive toxicity. However, it is still unclear how the structures of PFAS, such as carbon-chain length and functional groups, determine their reproductive toxicity.

METHODS AND RESULTS

By using a mouse-oocyte-in-vitro-maturation (IVM) system, we found the toxicity of two major categories of PFAS, perfluoroalkyl carboxylic acid (PFCA) and perfluoroalkyl sulfonic acid (PFSA), is elevated with increasing carbon-chain length and the inclusion of the sulfonate group. Specifically, at 600 μM, perfluorohexanesulfonic acid (PFHxS) and perfluorooctanesulfonic acid (PFOS) reduced the rates of both germinal-vesicle breakdown (GVBD) and polar-body extrusion (PBE) as well as enlarged polar bodies. However, the shorter PFSA, perfluorobutanesulfonic acid (PFBS), and all PFCA did not show similar adverse cytotoxicity. Further, we found that 600 μM PFHxS and PFOS exposure induced excess reactive oxygen species (ROS) and decreased mitochondrial membrane potential (MMP). Cytoskeleton analysis revealed that PFHxS and PFOS exposure induced chromosome misalignment, abnormal F-actin organization, elongated spindle formation, and symmetric division in the treated oocytes. These meiotic defects compromised oocyte developmental competence after parthenogenetic activation.

CONCLUSIONS

Our study provides new information on the structure-toxicity relationship of PFAS.

Actin limits egg aneuploidies associated with female reproductive aging

Aging-related centromeric cohesion loss underlies premature separation of sister chromatids and egg aneuploidy in reproductively older females. Here, we show that F-actin maintains chromatid association after cohesion deterioration in aged eggs. F-actin disruption in aged mouse eggs exacerbated untimely dissociation of sister chromatids, while its removal in young eggs induced extensive chromatid separation events generally only seen in advanced reproductive ages. In young eggs containing experimentally reduced cohesion, F-actin removal accelerated premature splitting and scattering of sister chromatids in a microtubule dynamics-dependent manner, suggesting that actin counteracts chromatid-pulling spindle forces. Consistently, F-actin stabilization restricted scattering of unpaired chromatids generated by complete degradation of centromeric cohesion proteins. We conclude that actin mitigates egg aneuploidies arising from age-related cohesion depletion by limiting microtubule-driven separation and dispersion of sister chromatids. This is supported by our finding that spindle-associated F-actin structures are disrupted in eggs of reproductively older females.

Unraveling the actin cytoskeleton in the malignant transformation of cholangiocyte biology

Correct actin cytoskeleton organization is vital in the liver organ homeostasis and disease control. Rearrangements of the actin cytoskeleton may play a vital role in the bile duct cells cholangiocytes. An abnormal actin network leads to aberrant cell morphology, deregulated signaling networks and ultimately triggering the development of cholangiocarcinoma (CCA) and paving the route for cancer cell dissemination (metastasis). In this review, we will outline alterations of the actin cytoskeleton and the potential role of this dynamic network in initiating CCA, as well as regulating the course of this malignancy. Actin rearrangements not only occur because of signaling pathways, but also regulate and modify cellular signaling. This emphasizes the importance of the actin cytoskeleton itself as cause for aberrant signaling and in promoting tumorigenic phenotypes. We will highlight the impact of aberrant signaling networks on the actin cytoskeleton and its rearrangement as potential cause for CCA. Often, these exact mechanisms in CCA are limited understood and still must be elucidated. Indeed, focusing future research on how actin affects and regulates other signaling pathways may provide more insights into the mechanisms of CCA development, progression, and metastasis. Moreover, manipulation of the actin cytoskeleton organization highlights the potential for a novel therapeutic area.

Dynamically regulated focal adhesions coordinate endothelial cell remodelling in developing vasculature

The assembly of a mature vascular network involves coordinated endothelial cell (EC) shape changes, including the process of EC elongation. How EC elongation is dynamically regulated in vivo is not fully understood. Here, we have generated a zebrafish mutant that is deficient for the integrin adaptor protein Talin 1 (Tln1). Using a new focal adhesion (FA) marker line expressing endothelial Vinculinb-eGFP, we demonstrate that EC FAs function dynamically and are lost in our tln1 mutants, allowing us to uncouple the primary roles of FAs in EC morphogenesis from the secondary effects that occur due to systemic vessel failure or loss of blood flow. Tln1 loss led to compromised F-actin rearrangements, perturbed EC elongation and disrupted cell-cell junction linearisation in vessel remodelling. Finally, chemical induction of actin polymerisation restored actin dynamics and EC elongation during vascular morphogenesis. Together, we identify that FAs are essential for EC elongation and junction linearisation in flow-pressured vessels and that they influence actin polymerisation in cellular morphogenesis. These observations can explain the severely compromised vessel beds and vascular leakage observed in mutant models that lack integrin signalling. This article has an associated 'The people behind the papers' interview.

Role of actin cytoskeleton in cargo delivery mediated by vertically aligned silicon nanotubes

Nanofabrication technologies have been recently applied to the development of engineered nano–bio interfaces for manipulating complex cellular processes. In particular, vertically configurated nanostructures such as nanoneedles (NNs) have been adopted for a variety of biological applications such as mechanotransduction, biosensing, and intracellular delivery. Despite their success in delivering a diverse range of biomolecules into cells, the mechanisms for NN-mediated cargo transport remain to be elucidated. Recent studies have suggested that cytoskeletal elements are involved in generating a tight and functional cell–NN interface that can influence cargo delivery. In this study, by inhibiting actin dynamics using two drugs—cytochalasin D (Cyto D) and jasplakinolide (Jas), we demonstrate that the actin cytoskeleton plays an important role in mRNA delivery mediated by silicon nanotubes (SiNTs). Specifically, actin inhibition 12 h before SiNT-cellular interfacing (pre-interface treatment) significantly dampens mRNA delivery (with efficiencies dropping to 17.2% for Cyto D and 33.1% for Jas) into mouse fibroblast GPE86 cells, compared to that of untreated controls (86.9%). However, actin inhibition initiated 2 h after the establishment of GPE86 cell–SiNT interface (post-interface treatment), has negligible impact on mRNA transfection, maintaining > 80% efficiency for both Cyto D and Jas treatment groups. The results contribute to understanding potential mechanisms involved in NN-mediated intracellular delivery, providing insights into strategic design of cell–nano interfacing under temporal control for improved effectiveness.

An insight into the recent developments in anti-infective potential of indole and associated hybrids

Prevention, accurate diagnosis, and effective treatment of infections are the main challenges in the overall management of infectious diseases. The best example is the ongoing SARs-COV-2(COVID-19) pandemic; the entire world is extremely worried about at present. Interestingly, heterocyclic moieties provide an ideal scaffold on which suitable pharmacophores can be designed to construct novel drugs. Indoles are amongst the most essential class of heteroaromatics in medicinal chemistry, which are ubiquitous across natural sources. The aforesaid derivatives have become invaluable scaffolds because of their wide spectrum therapeutic applications. Therefore, many researchers are focused on the design and synthesis of indole and associated hybrids of biological relevance. Hence, in the present review, we concisely discuss the indole containing natural sources, marketed drugs, clinical candidates, and their biological activities like antibacterial, antifungal, anti-TB, antiviral, antimalarial, and anti-leishmanial activities. The structure-activity relationships study of indole derivatives is also presented for a better understanding of the identified structures. The literature data presented for the anti-infective agents herein covers largely for the last twelve years.

Nanoantidote for repression of acidosis pH promoting COVID-19 infection

Acidosis, such as respiratory acidosis and metabolic acidosis, can be induced by coronavirus disease 2019 (COVID-19) infection and is associated with increased mortality in critically ill COVID-19 patients. It remains unclear whether acidosis further promotes SARS-CoV-2 infection in patients, making virus removal difficult. For antacid therapy, sodium bicarbonate poses great risks caused by sodium overload, bicarbonate side effects, and hypocalcemia. Therefore, new antacid antidote is urgently needed. Our study showed that an acidosis-related pH of 6.8 increases SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2) expression on the cell membrane by regulating intracellular microfilament polymerization, promoting SARS-CoV-2 pseudovirus infection. Based on this, we synthesized polyglutamic acid-PEG materials, used complexation of calcium ions and carboxyl groups to form the core, and adopted biomineralization methods to form a calcium carbonate nanoparticles (CaCO3-NPs) nanoantidote to neutralize excess hydrogen ions (H+), and restored the pH from 6.8 to approximately 7.4 (normal blood pH). CaCO3-NPs effectively prevented the heightened SARS-CoV-2 infection efficiency due to pH 6.8. Our study reveals that acidosis-related pH promotes SARS-CoV-2 infection, which suggests the existence of a positive feedback loop in which SARS-CoV-2 infection-induced acidosis enhances SARS-CoV-2 infection. Therefore, antacid therapy for acidosis COVID-19 patients is necessary. CaCO3-NPs may become an effective antacid nanoantidote superior to sodium bicarbonate.

Epithelial Cell-Like Elasticity Modulates Actin-Dependent E-Cadherin Adhesion Organization

E-cadherin adhesions are essential for cell-to-cell cohesion and mechanical coupling between epithelial cells and reside in a microenvironment that comprises the adjoining epithelial cells. While E-cadherin has been shown to be a mechanosensor, it is unknown if E-cadherin adhesions can differentially sense stiffness within the range of that of epithelial cells. A survey of literature shows that epithelial cells' Young's moduli of elasticity lie predominantly in the sub-kPa to few-kPa range, with cancer cells often being softer than noncancerous ones. Here, we devised oriented E-cadherin-coated soft silicone substrates with sub-kPa or few-kPa elasticity but with similar viscous moduli and found that E-cadherin adhesions differentially organize depending on the magnitude of epithelial cell-like elasticity. Our results show that the actin cytoskeleton organizes E-cadherin adhesions in two ways─by supporting irregularly shaped adhesions at localized regions of high actin density and linear shaped adhesions at the end of linear actin bundles. Linearly shaped E-cadherin adhesions associated with radially oriented actin─but not irregularly shaped E-cadherin adhesions associated with circumferential actin foci─were much more numerous on 2.4 kPa E-cadherin substrates compared to 0.3 kPa E-cadherin substrates. However, the total amount of E-cadherin in both types of adhesions taken together was similar on the 0.3 and 2.4 kPa E-cadherin substrates across many cells. Our results show how the distribution of E-cadherin adhesions, supported by actin density and architecture, is modulated by epithelial cell-like elasticity and have significant implications for disease states like carcinomas characterized by altered epithelial cell elasticity.

Simultaneous stabilization of actin cytoskeleton in multiple nephron-specific cells protects the kidney from diverse injury

Chronic kidney diseases and acute kidney injury are mechanistically distinct kidney diseases. While chronic kidney diseases are associated with podocyte injury, acute kidney injury affects renal tubular epithelial cells. Despite these differences, a cardinal feature of both acute and chronic kidney diseases is dysregulated actin cytoskeleton. We have shown that pharmacological activation of GTPase dynamin ameliorates podocyte injury in murine models of chronic kidney diseases by promoting actin polymerization. Here we establish dynamin's role in modulating stiffness and polarity of renal tubular epithelial cells by crosslinking actin filaments into branched networks. Activation of dynamin's crosslinking capability by a small molecule agonist stabilizes the actomyosin cortex of the apical membrane against injury, which in turn preserves renal function in various murine models of acute kidney injury. Notably, a dynamin agonist simultaneously attenuates podocyte and tubular injury in the genetic murine model of Alport syndrome. Our study provides evidence for the feasibility and highlights the benefits of novel holistic nephron-protective therapies.

Photoacoustic and magnetic resonance imaging-based gene and photothermal therapy using mesoporous nanoagents

The integration of photothermal therapy (PTT) with gene therapy (GT) in a single nanoscale platform demonstrates great potential in cancer therapy. Porous iron oxide nanoagents (PIONs) are widely used as magnetic nanoagents in the drug delivery field and also serve as a photothermal nanoagent for photothermal therapy. However, the therapeutic efficacy of PIONs-mediated GT has not been studied. The long noncoding RNA (lncRNA) CRYBG3 (LNC CRYBG3), a lncRNA induced by heavy ion irradiation in lung cancer cells, has been reported to directly bind to globular actin (G-actin) and cause degradation of cytoskeleton and blocking of cytokinesis, thus indicating its potential for use in GT by simulating the effect of heavy ion irradiation and functioning as an antitumor drug. In the present study, we investigated the possibility of combining PIONs-mediated PTT and LNC CRYBG3-mediated GT to destroy non-small cell lung cancer (NSCLC) cells both in vitro and in vivo. The combination therapy showed a high cancer cell killing efficacy, and the cure rate was better than that achieved using PTT or GT alone. Moreover, as a type of magnetic nanoagent, PIONs can be used for magnetic resonance imaging (MRI) and photoacoustic imaging (PAI) both in vitro and in vivo. These findings indicate that the new combination therapy has high potential for cancer treatment.

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LNC CRYBG3 induced by heavy ion irradiation can cause cytoskeleton degradation and function as an antitumor drug.

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pcDNA3.1-LNC CRYBG3 delivered by PIONs can escape from lysosomes to facilitate plasmid release when exposed to NIR.

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The combination of PIONs-mediated PTT and LNC CRYBG3-mediated GT presents both diagnosis and treatment potential.

The prolyl-isomerase PIN1 is essential for nuclear Lamin-B structure and function and protects heterochromatin under mechanical stress

Chromatin organization plays a crucial role in tissue homeostasis. Heterochromatin relaxation and consequent unscheduled mobilization of transposable elements (TEs) are emerging as key contributors of aging and aging-related pathologies, including Alzheimer's disease (AD) and cancer. However, the mechanisms governing heterochromatin maintenance or its relaxation in pathological conditions remain poorly understood. Here we show that PIN1, the only phosphorylation-specific cis/trans prolyl isomerase, whose loss is associated with premature aging and AD, is essential to preserve heterochromatin. We demonstrate that this PIN1 function is conserved from Drosophila to humans and prevents TE mobilization-dependent neurodegeneration and cognitive defects. Mechanistically, PIN1 maintains nuclear type-B Lamin structure and anchoring function for heterochromatin protein 1α (HP1α). This mechanism prevents nuclear envelope alterations and heterochromatin relaxation under mechanical stress, which is a key contributor to aging-related pathologies.

Cytoskeleton integrity influences XRCC1 and PCNA dynamics at DNA damage

On induction of DNA damage with 405-nm laser light, proteins involved in base excision repair (BER) are recruited to DNA lesions. We find that the dynamics of factors typical of either short-patch (XRCC1) or long-patch (PCNA) BER are altered by chemicals that perturb actin or tubulin polymerization in human cells. Whereas the destabilization of actin filaments by latrunculin B, cytochalasin B, or Jasplakinolide decreases BER factor accumulation at laser-induced damage, inhibition of tubulin polymerization by nocodazole increases it. We detect no recruitment of actin to sites of laser-induced DNA damage, yet the depolymerization of cytoplasmic actin filaments elevates both actin and tubulin signals in the nucleus. While published evidence suggested a positive role for F-actin in double-strand break repair in mammals, the enrichment of actin in budding yeast nuclei interferes with BER, augmenting sensitivity to Zeocin. Our quantitative imaging results suggest that the depolymerization of cytoplasmic actin may compromise BER efficiency in mammals not only due to elevated levels of nuclear actin but also of tubulin, linking cytoskeletal integrity to BER.

The roles of nuclear myosin in the DNA damage response

Myosin within the nucleus has often been overlooked due to their importance in cytoplasmic processes and a lack of investigation. However, more recently, it has been shown that their nuclear roles are just as fundamental to cell function and survival with roles in transcription, DNA damage and viral replication. Myosins can act as molecular transporters and anchors that rely on their actin binding and ATPase capabilities. Their roles within the DNA damage response can varies from a transcriptional response, moving chromatin and stabilizing chromosome contacts. This review aims to highlight their key roles in the DNA damage response and how they impact nuclear organization and transcription.

Nuclear Lamin A/C Expression Is a Key Determinant of Paclitaxel Sensitivity

Paclitaxel is a key member of the Taxane (paclitaxel [originally named taxol], docetaxel/Taxotere) family of successful drugs used in the current treatment of several solid tumors, including ovarian cancer. The molecular target of paclitaxel has been identified as tubulin, and paclitaxel binding alters the dynamics and thus stabilizes microtubule bundles. Traditionally, the anticancer mechanism of paclitaxel has been thought to originate from its interfering with the role of microtubules in mitosis, resulting in mitotic arrest and subsequent apoptosis. However, recent evidence suggests that paclitaxel operates in cancer therapies via an as-yet-undefined mechanism rather than as a mitotic inhibitor. We found that paclitaxel caused a striking break up of nuclei (referred to as multimicronucleation) in malignant ovarian cancer cells but not in normal cells, and susceptibility to undergo nuclear fragmentation and cell death correlated with a reduction in nuclear lamina proteins, lamin A/C. Lamin A/C proteins are commonly lost, reduced, or heterogeneously expressed in ovarian cancer, accounting for the aberration of nuclear shape in malignant cells. Mouse ovarian epithelial cells isolated from lamin A/C-null mice were highly sensitive to paclitaxel and underwent nuclear breakage, compared to control wild-type cells. Forced overexpression of lamin A/C led to resistance to paclitaxel-induced nuclear breakage in cancer cells. Additionally, paclitaxel-induced multimicronucleation occurred independently of cell division that was achieved by either the withdrawal of serum or the addition of mitotic inhibitors. These results provide a new understanding for the mitotis-independent mechanism for paclitaxel killing of cancer cells, where paclitaxel induces nuclear breakage in malignant cancer cells that have a malleable nucleus but not in normal cells that have a stiffer nuclear envelope. As such, we identify that reduced nuclear lamin A/C protein levels correlate with nuclear shape deformation and are a key determinant of paclitaxel sensitivity of cancer cells.

Dynamic intracellular mechanical cues facilitate collective signaling responses

Collective behavior emerges in diverse life machineries, e.g., the immune responses to dynamic stimulations. The essential questions that arise here are that whether and how cells in vivo collectively respond to stimulation frequencies higher than their intrinsic natural values, e.g., the acute inflammation conditions. In this work, we systematically studied morphological and signaling responses of population fibroblasts in an interconnected cell monolayer and uncovered that, besides the natural NF-κB oscillation frequency of 1/90 min⁻¹, collective signaling response emerges in the cell monolayer at 1/20 min⁻¹ TNF-α input periodicity as well. Using a customized microfluidic device, we independently induced dynamic chemical stimulation and cytoskeleton reorganization on the stand-alone cells to exclude the effect of cell-cell communication. Our results reveal that, at this particular frequency, chemical stimulation is translated into dynamic intracellular mechanical cues through RAC1-medicated induction of dynamic cell-cell connections and cytoskeleton reorganizations, which synergize with chemical input to facilitate collective signaling responses.

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Dynamic intracellular mechanical cues facilitate collective cellular responses

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The dynamic chemical stimulations are translated into intracellular mechanical cues

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The synergy between dynamic mechanical and chemical signal plays crucial roles

YAP-TEAD1 control of cytoskeleton dynamics and intracellular tension guides human pluripotent stem cell mesoderm specification

The tight regulation of cytoskeleton dynamics is required for a number of cellular processes, including migration, division and differentiation. YAP-TEAD respond to cell-cell interaction and to substrate mechanics and, among their downstream effects, prompt focal adhesion (FA) gene transcription, thus contributing to FA-cytoskeleton stability. This activity is key to the definition of adult cell mechanical properties and function. Its regulation and role in pluripotent stem cells are poorly understood. Human PSCs display a sustained basal YAP-driven transcriptional activity despite they grow in very dense colonies, indicating these cells are insensitive to contact inhibition. PSC inability to perceive cell-cell interactions can be restored by tampering with Tankyrase enzyme, thus favouring AMOT inhibition of YAP function. YAP-TEAD complex is promptly inactivated when germ layers are specified, and this event is needed to adjust PSC mechanical properties in response to physiological substrate stiffness. By providing evidence that YAP-TEAD1 complex targets key genes encoding for proteins involved in cytoskeleton dynamics, we suggest that substrate mechanics can direct PSC specification by influencing cytoskeleton arrangement and intracellular tension. We propose an aberrant activation of YAP-TEAD1 axis alters PSC potency by inhibiting cytoskeleton dynamics, thus paralyzing the changes in shape requested for the acquisition of the given phenotype.

Genomic and Targeted Approaches Unveil the Cell Membrane as a Major Target of the Antifungal Cytotoxin Amantelide A

Amantelide A, a polyhydroxylated macrolide isolated from a marine cyanobacterium, displays broad-spectrum activity against mammalian cells, bacterial pathogens, and marine fungi. We conducted comprehensive mechanistic studies to identify the molecular targets and pathways affected by amantelide A. Our investigations relied on chemical structure similarities with compounds of known mechanisms, yeast knockout mutants, yeast chemogenomic profiling, and direct biochemical and biophysical methods. We established that amantelide A exerts its antifungal action by binding to ergosterol-containing membranes followed by pore formation and cell death, a mechanism partially shared with polyene antifungals. Binding assays demonstrated that amantelide A also binds to membranes containing epicholesterol or mammalian cholesterol, thus suggesting that the cytotoxicity to mammalian cells might be due to its affinity to cholesterol-containing membranes. However, membrane interactions were not completely dependent on sterols. Yeast chemogenomic profiling suggested additional direct or indirect effects on actin. Accordingly, we performed actin polymerization assays, which suggested that amantelide A also promotes actin polymerization in cell-free systems. However, the C-33 acetoxy derivative amantelide B showed a similar effect on actin dynamics in vitro but no significant activity against yeast. Overall, these studies suggest that the membrane effects are the most functionally relevant for amantelide A mechanism of action.

Developmental clock and mechanism of de novo polarization of the mouse embryo

Embryo polarization is critical for mouse development; however, neither the regulatory clock nor the molecular trigger that it activates is known. Here, we show that the embryo polarization clock reflects the onset of zygotic genome activation, and we identify three factors required to trigger polarization. Advancing the timing of transcription factor AP-2 gamma (Tfap2c) and TEA domain transcription factor 4 (Tead4) expression in the presence of activated Ras homolog family member A (RhoA) induces precocious polarization as well as subsequent cell fate specification and morphogenesis. Tfap2c and Tead4 induce expression of actin regulators that control the recruitment of apical proteins on the membrane, whereas RhoA regulates their lateral mobility, allowing the emergence of the apical domain. Thus, Tfap2c, Tead4, and RhoA are regulators for the onset of polarization and cell fate segregation in the mouse.

Daam2 couples translocation and clustering of Wnt receptor signalosomes through Rac1

Wnt signaling plays a critical role in development across species and is dysregulated in a host of human diseases. A key step in signal transduction is the formation of Wnt receptor signalosomes, during which a large number of components translocate to the membrane, cluster together and amplify downstream signaling. However, the molecular processes that coordinate these events remain poorly defined. Here, we show that Daam2 regulates canonical Wnt signaling via the PIP₂-PIP5K axis through its association with Rac1. Clustering of Daam2-mediated Wnt receptor complexes requires both Rac1 and PIP5K, and PIP5K promotes membrane localization of these complexes in a Rac1-dependent manner. Importantly, the localization of Daam2 complexes and Daam2-mediated canonical Wnt signaling is dependent upon actin polymerization. These studies - in chick spinal cord and human and monkey cell lines - highlight novel roles for Rac1 and the actin cytoskeleton in the regulation of canonical Wnt signaling and define Daam2 as a key scaffolding hub that coordinates membrane translocation and signalosome clustering.

In vitro and in vivo effects of inhibitors on actin and myosin

The interaction of actin and myosin is essential for cell migration. We have identified kaempferol and pentahalogenated pseudilins as efficient inhibitors of migration of MDA-MB-231 breast adenocarcinoma cells. The compounds were studied with respect to possible effects on myosin-2-ATPase activity. The pentahalogenated pseudilins inhibited the enzyme activity in vitro. Flavonoids showed no effect on enzyme activity. The polymerization dynamics of actin was measured to test whether the integrity of F-actin is essential for the migration of MDA-MB-231 cells. Quercetin and kaempferol depolymerized F-actin with similar efficiencies as found for the pentahalogenated pseudilins, whereas epigallocatechin showed the weakest effect. As the inhibitory effect on cell migration may be caused by a toxic effect, we have performed a cytotoxicity test and, furthermore, investigated the influence of the test compounds on cardiac function in eleutheroembryos of medaka (Oryzias latipes). Compared with the pentahalogenated pseudilins, the cytotoxic and cardiotoxic effects of flavonoids on medaka embryos were found to be moderate.

Quantitative Bio-Imaging Tools to Dissect the Interplay of Membrane and Cytoskeletal Actin Dynamics in Immune Cells

Cellular function is reliant on the dynamic interplay between the plasma membrane and the actin cytoskeleton. This critical relationship is of particular importance in immune cells, where both the cytoskeleton and the plasma membrane work in concert to organize and potentiate immune signaling events. Despite their importance, there remains a critical gap in understanding how these respective dynamics are coupled, and how this coupling in turn may influence immune cell function from the bottom up. In this review, we highlight recent optical technologies that could provide strategies to investigate the simultaneous dynamics of both the cytoskeleton and membrane as well as their interplay, focusing on current and future applications in immune cells. We provide a guide of the spatio-temporal scale of each technique as well as highlighting novel probes and labels that have the potential to provide insights into membrane and cytoskeletal dynamics. The quantitative biophysical tools presented here provide a new and exciting route to uncover the relationship between plasma membrane and cytoskeletal dynamics that underlies immune cell function.

Tavarua Deoxyriboside A and Jasplakinolide as Potential Neuroprotective Agents: Effects on Cellular Models of Oxidative Stress and Neuroinflammation

The oceans harbor a great reservoir of molecules with unknown bioactivities, which could be useful for the treatment of illnesses that nowadays have no cure, such as neurodegenerative diseases. In this work, we evaluated the neuroprotective potential of the marine Fijian compounds tavarua deoxyriboside A and jasplakinolide against oxidative stress and neuroinflammation, crucial mechanisms in neurodegeneration. Both metabolites protected SH-SY5Y human neuroblastoma cells from H₂O₂ damage, improving mitochondrial function and activating the antioxidant systems of cells. These effects were mediated by their ability of inducing Nrf2 translocation. In BV2 microglial cells activated with lipopolysaccharide, Fijian metabolites also displayed promising results, decreasing the release of proinflammatory mediators (ROS, NO, cytokines) through the reduction of gp91 and NFkB-p65 expression. Finally, we performed a coculture among both cell lines, in which treatment with compounds protected SH-SY5Y cells from activated microglia, corroborating their neuroprotective effects. These results suggest that tavarua deoxyriboside A and jasplakinolide could be used as candidate molecules for further studies against neurodegeneration.

Primary Cilia, Ciliogenesis and the Actin Cytoskeleton: A Little Less Resorption, A Little More Actin Please

Primary cilia are microtubule-based organelles that extend from the apical surface of most mammalian cells, forming when the basal body (derived from the mother centriole) docks at the apical cell membrane. They act as universal cellular "antennae" in vertebrates that receive and integrate mechanical and chemical signals from the extracellular environment, serving diverse roles in chemo-, mechano- and photo-sensation that control developmental signaling, cell polarity and cell proliferation. Mutations in ciliary genes cause a major group of inherited developmental disorders called ciliopathies. There are very few preventative treatments or new therapeutic interventions that modify disease progression or the long-term outlook of patients with these conditions. Recent work has identified at least four distinct but interrelated cellular processes that regulate cilia formation and maintenance, comprising the cell cycle, cellular proteostasis, signaling pathways and structural influences of the actin cytoskeleton. The actin cytoskeleton is composed of microfilaments that are formed from filamentous (F) polymers of globular G-actin subunits. Actin filaments are organized into bundles and networks, and are attached to the cell membrane, by diverse cross-linking proteins. During cell migration, actin filament bundles form either radially at the leading edge or as axial stress fibers. Early studies demonstrated that loss-of-function mutations in ciliopathy genes increased stress fiber formation and impaired ciliogenesis whereas pharmacological inhibition of actin polymerization promoted ciliogenesis. These studies suggest that polymerization of the actin cytoskeleton, F-actin branching and the formation of stress fibers all inhibit primary cilium formation, whereas depolymerization or depletion of actin enhance ciliogenesis. Here, we review the mechanistic basis for these effects on ciliogenesis, which comprise several cellular processes acting in concert at different timescales. Actin polymerization is both a physical barrier to both cilia-targeted vesicle transport and to the membrane remodeling required for ciliogenesis. In contrast, actin may cause cilia loss by localizing disassembly factors at the ciliary base, and F-actin branching may itself activate the YAP/TAZ pathway to promote cilia disassembly. The fundamental role of actin polymerization in the control of ciliogenesis may present potential new targets for disease-modifying therapeutic approaches in treating ciliopathies.

The CAR T-Cell Mechanoimmunology at a Glance

Chimeric antigen receptor (CAR) T-cell transfer is a novel paradigm of adoptive T-cell immunotherapy. When coming into contact with a target cancer cell, CAR T-cell forms a nonclassical immunological synapse with the cancer cell and dynamically orchestrates multiple critical forces to commit cytotoxic immune function. Such an immunologic process involves a force transmission in the CAR and a spatiotemporal remodeling of cell cytoskeleton to facilitate CAR activation and CAR T-cell cytotoxic function. Yet, the detailed understanding of such mechanotransduction at the interface between the CAR T-cell and the target cell, as well as its molecular structure and signaling, remains less defined and is just beginning to emerge. This article summarizes the basic mechanisms and principles of CAR T-cell mechanoimmunology, and various lessons that can be comparatively learned from interrogation of mechanotransduction at the immunological synapse in normal cytotoxic T-cell. The recent development and future application of novel bioengineering tools for studying CAR T-cell mechanoimmunology is also discussed. It is believed that this progress report will shed light on the CAR T-cell mechanoimmunology and encourage future researches in revealing the less explored yet important mechanosensing and mechanotransductive mechanisms involved in CAR T-cell immuno-oncology.

Elasticity spectra as a tool to investigate actin cortex mechanics

Background

The mechanical properties of single living cells have proven to be a powerful marker of the cell physiological state. The use of nanoindentation-based single cell force spectroscopy provided a wealth of information on the elasticity of cells, which is still largely to be exploited. The simplest model to describe cell mechanics is to treat them as a homogeneous elastic material and describe it in terms of the Young’s modulus. Beside its simplicity, this approach proved to be extremely informative, allowing to assess the potential of this physical indicator towards high throughput phenotyping in diagnostic and prognostic applications.

Results

Here we propose an extension of this analysis to explicitly account for the properties of the actin cortex. We present a method, the Elasticity Spectra, to calculate the apparent stiffness of the cell as a function of the indentation depth and we suggest a simple phenomenological approach to measure the thickness and stiffness of the actin cortex, in addition to the standard Young’s modulus.

Conclusions

The Elasticity Spectra approach is tested and validated on a set of cells treated with cytoskeleton-affecting drugs, showing the potential to extend the current representation of cell mechanics, without introducing a detailed and complex description of the intracellular structure.

The Huntingtin-interacting protein SETD2/HYPB is an actin lysine methyltransferase

The methyltransferase SET domain-containing 2 (SETD2) was originally identified as Huntingtin (HTT) yeast partner B. However, a SETD2 function associated with the HTT scaffolding protein has not been elucidated, and no linkage between HTT and methylation has yet been uncovered. Here, we show that SETD2 is an actin methyltransferase that trimethylates lysine-68 (ActK68me3) in cells via its interaction with HTT and the actin-binding adapter HIP1R. ActK68me3 localizes primarily to the insoluble F-actin cytoskeleton in cells and regulates actin polymerization/depolymerization dynamics. Disruption of the SETD2-HTT-HIP1R axis inhibits actin methylation, causes defects in actin polymerization, and impairs cell migration. Together, these data identify SETD2 as a previously unknown HTT effector regulating methylation and polymerization of actin filaments and provide new avenues for understanding how defects in SETD2 and HTT drive disease via aberrant cytoskeletal methylation.

CB1-receptor-mediated inhibitory LTD triggers presynaptic remodeling via protein synthesis and ubiquitination

Long-lasting forms of postsynaptic plasticity commonly involve protein synthesis-dependent structural changes of dendritic spines. However, the relationship between protein synthesis and presynaptic structural plasticity remains unclear. Here, we investigated structural changes in cannabinoid-receptor 1 (CB₁)-mediated long-term depression of inhibitory transmission (iLTD), a form of presynaptic plasticity that involves a protein-synthesis-dependent long-lasting reduction in GABA release. We found that CB₁-iLTD in acute rat hippocampal slices was associated with protein synthesis-dependent presynaptic structural changes. Using proteomics, we determined that CB₁ activation in hippocampal neurons resulted in increased ribosomal proteins and initiation factors, but decreased levels of proteins involved in regulation of the actin cytoskeleton, such as ARPC2 and WASF1/WAVE1, and presynaptic release. Moreover, while CB₁-iLTD increased ubiquitin/proteasome activity, ubiquitination but not proteasomal degradation was critical for structural and functional presynaptic CB₁-iLTD. Thus, CB₁-iLTD relies on both protein synthesis and ubiquitination to elicit structural changes that underlie long-term reduction of GABA release.

Genetic suppression of defective profilin by attenuated Myosin II reveals a potential role for Myosin II in actin dynamics in vivo in fission yeast

The actin cytoskeleton plays a variety of roles in eukaryotic cell physiology, ranging from cell polarity and migration to cytokinesis. Key to the function of the actin cytoskeleton is the mechanisms that control its assembly, stability, and turnover. Through genetic analyses in Schizosaccharomyces pombe, we found that myo2-S1 (myo2-G515D), a Myosin II mutant allele, was capable of rescuing lethality caused by partial defects in actin nucleation/stability caused, for example, through compromised function of the actin-binding protein Cdc3-profilin. The mutation in myo2-S1 affects the activation loop of Myosin II, which is involved in physical interaction with subdomain 1 of actin and in stimulating the ATPase activity of Myosin. Consistently, actomyosin rings in myo2-S1 cell ghosts were unstable and severely compromised in contraction on ATP addition. These studies strongly suggest a role for Myo2 in actin cytoskeletal disassembly and turnover in vivo, and that compromise of this activity leads to genetic suppression of mutants defective in actin filament assembly/stability at the division site.

Synapse elimination activates a coordinated homeostatic presynaptic response in an autaptic circuit

The number of synapses present in a neuronal circuit is not fixed. Neurons must compensate for changes in connectivity caused by synaptic pruning, learning processes or pathological conditions through the constant adjustment of the baseline level of neurotransmission. Here, we show that cholinergic neurons grown in an autaptic circuit in the absence of glia sense the loss of half of their synaptic contacts triggered by exposure to peptide p4.2, a C-terminal fragment of SPARC. Synaptic elimination is driven by a reorganization of the periodic F-actin cytoskeleton present along neurites, and occurs without altering the density of postsynaptic receptors. Neurons recover baseline neurotransmission through a homeostatic presynaptic response that consists of the coordinated activation of rapid synapse formation and an overall potentiation of presynaptic calcium influx. These results demonstrate that neurons establishing autaptic connections continuously sense and adjust their synaptic output by tweaking the number of functional contacts and neurotransmitter release probability.

Cecilia Velasco and Artur Llobet study how autapses respond to synapse elimination. They employ microisland cultures free of glial cells, treat with a SPARC-derived peptide and show that neurons forming autaptic circuits continuously sense and regulate the number of contacts and neurotransmitter release.

Role of Junction-Mediating and Regulatory Protein in the Pathogenesis of Glucocorticoid-Induced Endothelial Cell Lesions

Objective

Nontraumatic osteonecrosis of the femoral head (ONFH) is one of the most common diseases in orthopaedics. The damage to vascular endothelial (VE) cells caused by glucocorticoids (GC) has been reported as a possible mechanism of pathogenesis for ONFH. Junction‐mediating and regulatory protein (JMY), originally identified as a p53 coactivator, plays prominent roles in the DNA damage response and in cell motility. This study aimed to discover the role of JMY in the pathogenesis of GC‐induced endothelial cell lesions.

Methods

High‐throughput RNA sequencing was performed to identify the differentially expressed genes between GC‐treated human umbilical vein endothelial cells (HUVEC) and control cells. JMY knockdown and overexpressing HUVEC lines were treated with GC. Cell proliferation was examined with a survival cell count assay (Cell Counting Kit‐8, CCK‐8); cell apoptosis was measured by flow cytometry; a scarification assay was used to detect the capability of cell migration; a Transwell chamber assay was done to detect the cell motility . Differential expression of cell protein was detected by western blot.

Results

A total of 1561 differential genes were obtained through transcription sequencing, of which 789 mRNA were upregulated and 772 mRNA were downregulated in the GC‐treated HUVEC compared with the control cells. CCK‐8 assay results showed that: without GC treatment, overexpression or knockdown of JMY did not affect the proliferation activity of HUVEC. In the presence of GC treatment, the proliferation activity of HUVEC in the JMY knockdown group was significantly higher than that in the control group (P < 0.01). The proliferation activity of HUVEC in the overexpression JMY group was significantly lower than that in the control group (P < 0.01). The results of flow cytometry showed that without GC treatment, overexpression or knockdown of JMY did not affect the apoptosis proportion of HUVEC. With GC treatment, the apoptosis proportion of HUVEC in the JMY knockdown group was significantly lower than that in the control group (P < 0.01), and the apoptosis proportion of HUVEC in the overexpression JMY group was significantly higher than that in the control group (P < 0.01). Western blot results showed that with GC treatment, the JMY expression level of HUVEC increased with the reaction time. Moreover, the distribution of JMY was mainly concentrated in the nucleus. The expression level of Bax also increased with the reaction time. With GC treatment, overexpression of JMY could significantly increase the expression of Bax in HUVEC. JMY knockdown could reduce the expression of Bax in HUVEC. In the absence of GC treatment, HUVEC overexpression or knockdown of JMY did not affect the expression of Bax. The results of scarification and Transwell chamber assays showed that: without GC treatment, JMY knockdown could significantly decrease the cell motility and increase the expression level of VE‐cadherin in HUVEC; with GC treatment, JMY knockdown in HUVEC had lower cell motility compared with the control group (P < 0.01).

Conclusion

Glucocorticoids can induce the HUVEC apoptosis, and reduce its proliferation, cell motility. Our results mainly confirmed the role of JMY in the pathogenesis of GC‐inducing lesions in HUVEC. GC act on HUVEC, inducing cell damage. Following the event of cell damage, JMY levels upregulate in the nucleus to induce transcription of Bax, triggering apoptosis. JMY can also regulate HUVEC motility via its regulation of VE‐cadherin levels.

The malaria parasite Plasmodium falciparum in red blood cells selectively takes up serum proteins that affect host pathogenicity

Background

The malaria parasite Plasmodium falciparum is a protozoan that develops in red blood cells (RBCs) and requires various host factors. For its development in RBCs, nutrients not only from the RBC cytosol but also from the extracellular milieu must be acquired. Although the utilization of host nutrients by P. falciparum has been extensively analysed, only a few studies have reported its utilization of host serum proteins. Hence, the aim of the current study was to comprehensively identify host serum proteins taken up by P. falciparum parasites and to elucidate their role in pathogenesis.

Methods

Plasmodium falciparum was cultured with human serum in vitro. Uptake of serum proteins by parasites was comprehensively determined via shotgun liquid chromatography–mass spectrometry/mass spectrometry and western blotting. The calcium ion concentration in serum was also evaluated, and coagulation activity of the parasite lysate was assessed.

Results

Three proteins, vitamin K-dependent protein S, prothrombin, and vitronectin, were selectively internalized under sufficient Ca²⁺ levels in the culture medium. The uptake of these proteins was initiated before DNA replication, and increased during the trophozoite and schizont stages, irrespective of the assembly/disassembly of actin filaments. Coagulation assay revealed that prothrombin was activated and thereby induced blood coagulation.

Conclusions

Serum proteins were taken up by parasites under culture conditions with sufficient Ca²⁺ levels. This uptake phenomenon was associated with their pathogenicity.

Qualitative analysis of contribution of intracellular skeletal changes to cellular elasticity

Cells are dynamic structures that continually generate and sustain mechanical forces within their environments. Cells respond to mechanical forces by changing their shape, moving, and differentiating. These reactions are caused by intracellular skeletal changes, which induce changes in cellular mechanical properties such as stiffness, elasticity, viscoelasticity, and adhesiveness. Interdisciplinary research combining molecular biology with physics and mechanical engineering has been conducted to characterize cellular mechanical properties and understand the fundamental mechanisms of mechanotransduction. In this review, we focus on the role of cytoskeletal proteins in cellular mechanics. The specific role of each cytoskeletal protein, including actin, intermediate filaments, and microtubules, on cellular elasticity is summarized along with the effects of interactions between the fibers.

Structural Effects and Functional Implications of Phalloidin and Jasplakinolide Binding to Actin Filaments

Actin undergoes structural transitions during polymerization, ATP hydrolysis, and subsequent release of inorganic phosphate. Several actin-binding proteins sense specific states during this transition and can thus target different regions of the actin filament. Here, we show in atomic detail that phalloidin, a mushroom toxin that is routinely used to stabilize and label actin filaments, suspends the structural changes in actin, likely influencing its interaction with actin-binding proteins. Furthermore, high-resolution cryoelectron microscopy structures reveal structural rearrangements in F-actin upon inorganic phosphate release in phalloidin-stabilized filaments. We find that the effect of the sponge toxin jasplakinolide differs from the one of phalloidin, despite their overlapping binding site and similar interactions with the actin filament. Analysis of structural conformations of F-actin suggests that stabilizing agents trap states within the natural conformational space of actin.

Cytoskeletal Proteins in Cancer and Intracellular Stress: A Therapeutic Perspective

Cytoskeletal proteins, which consist of different sub-families of proteins including microtubules, actin and intermediate filaments, are essential for survival and cellular processes in both normal as well as cancer cells. However, in cancer cells, these mechanisms can be altered to promote tumour development and progression, whereby the functions of cytoskeletal proteins are co-opted to facilitate increased migrative and invasive capabilities, proliferation, as well as resistance to cellular and environmental stresses. Herein, we discuss the cytoskeletal responses to important intracellular stresses (such as mitochondrial, endoplasmic reticulum and oxidative stresses), and delineate the consequences of these responses, including effects on oncogenic signalling. In addition, we elaborate how the cytoskeleton and its associated molecules present themselves as therapeutic targets. The potential and limitations of targeting new classes of cytoskeletal proteins are also explored, in the context of developing novel strategies that impact cancer progression.

Caveolin-1 Modulates Mechanotransduction Responses to Substrate Stiffness through Actin-Dependent Control of YAP

The transcriptional regulator YAP orchestrates many cellular functions, including tissue homeostasis, organ growth control, and tumorigenesis. Mechanical stimuli are a key input to YAP activity, but the mechanisms controlling this regulation remain largely uncharacterized. We show that CAV1 positively modulates the YAP mechanoresponse to substrate stiffness through actin-cytoskeleton-dependent and Hippo-kinase-independent mechanisms. RHO activity is necessary, but not sufficient, for CAV1-dependent mechanoregulation of YAP activity. Systematic quantitative interactomic studies and image-based small interfering RNA (siRNA) screens provide evidence that this actin-dependent regulation is determined by YAP interaction with the 14-3-3 protein YWHAH. Constitutive YAP activation rescued phenotypes associated with CAV1 loss, including defective extracellular matrix (ECM) remodeling. CAV1-mediated control of YAP activity was validated in vivo in a model of pancreatitis-driven acinar-to-ductal metaplasia. We propose that this CAV1-YAP mechanotransduction system controls a significant share of cell programs linked to these two pivotal regulators, with potentially broad physiological and pathological implications.