FAM110A promotes mitotic spindle formation by linking microtubules with actin cytoskeleton.

Precise segregation of chromosomes during mitosis requires assembly of a bipolar mitotic spindle followed by correct attachment of microtubules to the kinetochores. This highly spatiotemporally organized process is controlled by various mitotic kinases and molecular motors. We have recently shown that Casein Kinase 1 (CK1) promotes timely progression through mitosis by phosphorylating FAM110A leading to its enrichment at spindle poles. However, the mechanism by which FAM110A exerts its function in mitosis is unknown. Using structure prediction and a set of deletion mutants, we mapped here the interaction of the N- and C-terminal domains of FAM110A with actin and tubulin, respectively. Next, we found that the FAM110A-Δ40-61 mutant deficient in actin binding failed to rescue defects in chromosomal alignment caused by depletion of endogenous FAM110A. Depletion of FAM110A impaired assembly of F-actin in the proximity of spindle poles and was rescued by expression of the wild-type FAM110A, but not the FAM110A-Δ40-61 mutant. Purified FAM110A promoted binding of F-actin to microtubules as well as bundling of actin filaments in vitro. Finally, we found that the inhibition of CK1 impaired spindle actin formation and delayed progression through mitosis. We propose that CK1 and FAM110A promote timely progression through mitosis by mediating the interaction between spindle microtubules and filamentous actin to ensure proper mitotic spindle formation.

Intracellular delivery and deep tissue penetration of nucleoside triphosphates using photocleavable covalently bound dendritic polycations.

Nucleoside triphosphates (NTPs) are essential in various biological processes. Cellular or even organismal controlled delivery of NTPs would be highly desirable, yet in cellulo and in vivo applications are hampered owing to their negative charge leading to cell impermeability. NTP transporters or NTP prodrugs have been developed, but a spatial and temporal control of the release of the investigated molecules remains challenging with these strategies. Herein, we describe a general approach to enable intracellular delivery of NTPs using covalently bound dendritic polycations, which are derived from PAMAM dendrons and their guanidinium derivatives. By design, these modifications are fully removable through attachment on a photocage, ready to deliver the native NTP upon irradiation enabling spatiotemporal control over nucleotide release. We study the intracellular distribution of the compounds depending on the linker and dendron generation as well as side chain modifications. Importantly, as the polycation is bound covalently, these molecules can also penetrate deeply into the tissue of living organisms, such as zebrafish.

Nuclear actin dynamics and functions at a glance.

Actin is well known for its cytoskeletal functions, where it helps to control and maintain cell shape and architecture, as well as regulating cell migration and intracellular cargo transport, among others. However, actin is also prevalent in the nucleus, where genome-regulating roles have been described, including it being part of chromatin-remodeling complexes. More recently, with the help of advances in microscopy techniques and specialized imaging probes, direct visualization of nuclear actin filament dynamics has helped elucidate new roles for nuclear actin, such as in cell cycle regulation, DNA replication and repair, chromatin organization and transcriptional condensate formation. In this Cell Science at a Glance article, we summarize the known signaling events driving the dynamic assembly of actin into filaments of various structures within the nuclear compartment for essential genome functions. Additionally, we highlight the physiological role of nuclear F-actin in meiosis and early embryonic development.

ROCK1/2 signaling contributes to corticosteroid-refractory acute graft-versus-host disease.

Patients with corticosteroid-refractory acute graft-versus-host disease (aGVHD) have a low one-year survival rate. Identification and validation of novel targetable kinases in patients who experience corticosteroid-refractory-aGVHD may help improve outcomes. Kinase-specific proteomics of leukocytes from patients with corticosteroid-refractory-GVHD identified rho kinase type 1 (ROCK1) as the most significantly upregulated kinase. ROCK1/2 inhibition improved survival and histological GVHD severity in mice and was synergistic with JAK1/2 inhibition, without compromising graft-versus-leukemia-effects. ROCK1/2-inhibition in macrophages or dendritic cells prior to transfer reduced GVHD severity. Mechanistically, ROCK1/2 inhibition or ROCK1 knockdown interfered with CD80, CD86, MHC-II expression and IL-6, IL-1ß, iNOS and TNF production in myeloid cells. This was accompanied by impaired T cell activation by dendritic cells and inhibition of cytoskeletal rearrangements, thereby reducing macrophage and DC migration. NF-κB signaling was reduced in myeloid cells following ROCK1/2 inhibition. In conclusion, ROCK1/2 inhibition interferes with immune activation at multiple levels and reduces acute GVHD while maintaining GVL-effects, including in corticosteroid-refractory settings.

Nuclear actin polymerization rapidly mediates replication fork remodeling upon stress by limiting PrimPol activity.

Cells rapidly respond to replication stress actively slowing fork progression and inducing fork reversal. How replication fork plasticity is achieved in the context of nuclear organization is currently unknown. Using nuclear actin probes in living and fixed cells, we visualized nuclear actin filaments in unperturbed S phase and observed their rapid extension in number and length upon genotoxic treatments, frequently taking contact with replication factories. Chemically or genetically impairing nuclear actin polymerization shortly before these treatments prevents active fork slowing and abolishes fork reversal. Defective fork remodeling is linked to deregulated chromatin loading of PrimPol, which promotes unrestrained and discontinuous DNA synthesis and limits the recruitment of RAD51 and SMARCAL1 to nascent DNA. Moreover, defective nuclear actin polymerization upon mild replication interference induces chromosomal instability in a PRIMPOL-dependent manner. Hence, by limiting PrimPol activity, nuclear F-actin orchestrates replication fork plasticity and is a key molecular determinant in the rapid cellular response to genotoxic treatments.

Quantitative real-time in-cell imaging reveals heterogeneous clusters of proteins prior to condensation.

Our current understanding of biomolecular condensate formation is largely based on observing the final near-equilibrium condensate state. Despite expectations from classical nucleation theory, pre-critical protein clusters were recently shown to form under subsaturation conditions in vitro; if similar long-lived clusters comprising more than a few molecules are also present in cells, our understanding of the physical basis of biological phase separation may fundamentally change. Here, we combine fluorescence microscopy with photobleaching analysis to quantify the formation of clusters of NELF proteins in living, stressed cells. We categorise small and large clusters based on their dynamics and their response to p38 kinase inhibition. We find a broad distribution of pre-condensate cluster sizes and show that NELF protein cluster formation can be explained as non-classical nucleation with a surprisingly flat free-energy landscape for a wide range of sizes and an inhibition of condensation in unstressed cells.

The lysophosphatidic acid-regulated signal transduction network in ovarian cancer cells and its role in actomyosin dynamics, cell migration and entosis.

Lysophosphatidic acid (LPA) species accumulate in the ascites of ovarian high-grade serous cancer (HGSC) and are associated with short relapse-free survival. LPA is known to support metastatic spread of cancer cells by activating a multitude of signaling pathways via G-protein-coupled receptors of the LPAR family. Systematic unbiased analyses of the LPA-regulated signal transduction network in ovarian cancer cells have, however, not been reported to date. Methods: LPA-induced signaling pathways were identified by phosphoproteomics of both patient-derived and OVCAR8 cells, RNA sequencing, measurements of intracellular Ca2+ and cAMP as well as cell imaging. The function of LPARs and downstream signaling components in migration and entosis were analyzed by selective pharmacological inhibitors and RNA interference. Results: Phosphoproteomic analyses identified > 1100 LPA-regulated sites in > 800 proteins and revealed interconnected LPAR1, ROCK/RAC, PKC/D and ERK pathways to play a prominent role within a comprehensive signaling network. These pathways regulate essential processes, including transcriptional responses, actomyosin dynamics, cell migration and entosis. A critical component of this signaling network is MYPT1, a stimulatory subunit of protein phosphatase 1 (PP1), which in turn is a negative regulator of myosin light chain 2 (MLC2). LPA induces phosphorylation of MYPT1 through ROCK (T853) and PKC/ERK (S507), which is majorly driven by LPAR1. Inhibition of MYPT1, PKC or ERK impedes both LPA-induced cell migration and entosis, while interference with ROCK activity and MLC2 phosphorylation selectively blocks entosis, suggesting that MYPT1 figures in both ROCK/MLC2-dependent and -independent pathways. We finally show a novel pathway governed by LPAR2 and the RAC-GEF DOCK7 to be indispensable for the induction of entosis. Conclusion: We have identified a comprehensive LPA-induced signal transduction network controlling LPA-triggered cytoskeletal changes, cell migration and entosis in HGSC cells. Due to its pivotal role in this network, MYPT1 may represent a promising target for interfering with specific functions of PP1 essential for HGSC progression.

Formin-mediated nuclear actin at androgen receptors promotes transcription.

Steroid hormone receptors are ligand-binding transcription factors essential for mammalian physiology. The androgen receptor (AR) binds androgens mediating gene expression for sexual, somatic and behavioural functions, and is involved in various conditions including androgen insensitivity syndrome and prostate cancer1. Here we identified functional mutations in the formin and actin nucleator DAAM2 in patients with androgen insensitivity syndrome. DAAM2 was enriched in the nucleus, where its localization correlated with that of the AR to form actin-dependent transcriptional droplets in response to dihydrotestosterone. DAAM2 AR droplets ranged from 0.02 to 0.06 µm3 in size and associated with active RNA polymerase II. DAAM2 polymerized actin directly at the AR to promote droplet coalescence in a highly dynamic manner, and nuclear actin polymerization is required for prostate-specific antigen expression in cancer cells. Our data uncover signal-regulated nuclear actin assembly at a steroid hormone receptor necessary for transcription.

Spatiotemporal Regulation of FMNL2 by N-Terminal Myristoylation and C-Terminal Phosphorylation Drives Rapid Filopodia Formation.

The actin nucleating and polymerizing formin-like 2 (FMNL2) is upregulated in several cancers and has been shown to play important roles in cell migration, invasion, cell-cell adhesion and filopodia formation. Here, using structured illumination microscopy we show that FMNL2 promotes rapid and highly dynamic filopodia formation in epithelial cells while remaining on the tip of the growing filopodia. This filopodia tip localization depends fully on its N-terminal myristoylation. We further show that FMNL2-dependent filopodia formation requires its serine 1072 phosphorylation within the diaphanous-autoregulatory domain (DAD) by protein kinase C (PKC) α. Consistent with this, filopodia formation depends on PKC activity and PKCα localizes to the base of growing filopodia. Thus, a PKCα-FMNL2 signaling module spatiotemporally controls dynamic filopodia formation.

Replication fork plasticity upon replication stress requires rapid nuclear actin polymerization.

Cells rapidly respond to replication stress actively slowing fork progression and inducing fork reversal. How replication fork plasticity is achieved in the context of nuclear organization is currently unknown. Using nuclear actin probes in living and fixed cells, we visualized nuclear actin filaments in unperturbed S phase, rapidly extending in number and thickness upon genotoxic treatments, and taking frequent contact with replication factories. Chemically or genetically impairing nuclear actin polymerization shortly before these treatments prevents active fork slowing and abolishes fork reversal. Defective fork plasticity is linked to reduced recruitment of RAD51 and SMARCAL1 to nascent DNA. Conversely, PRIMPOL gains access to replicating chromatin, promoting unrestrained and discontinuous DNA synthesis, which is associated with increased chromosomal instability and decreased cellular resistance to replication stress. Hence, nuclear F-actin orchestrates replication fork plasticity and is a key molecular determinant in the rapid cellular response to genotoxic treatments.

Stabilization of membrane topologies by proteinaceous remorin scaffolds.

In plants, the topological organization of membranes has mainly been attributed to the cell wall and the cytoskeleton. Additionally, few proteins, such as plant-specific remorins have been shown to function as protein and lipid organizers. Root nodule symbiosis requires continuous membrane re-arrangements, with bacteria being finally released from infection threads into membrane-confined symbiosomes. We found that mutations in the symbiosis-specific SYMREM1 gene result in highly disorganized perimicrobial membranes. AlphaFold modelling and biochemical analyses reveal that SYMREM1 oligomerizes into antiparallel dimers and may form a higher-order membrane scaffolding structure. This was experimentally confirmed when expressing this and other remorins in wall-less protoplasts is sufficient where they significantly alter and stabilize de novo membrane topologies ranging from membrane blebs to long membrane tubes with a central actin filament. Reciprocally, mechanically induced membrane indentations were equally stabilized by SYMREM1. Taken together we describe a plant-specific mechanism that allows the stabilization of large-scale membrane conformations independent of the cell wall.

Vesicle-Associated Actin Assembly by Formins Promotes TGFß-Induced ANGPTL4 Trafficking, Secretion and Cell Invasion.

Vesicle trafficking has emerged as an important process driving tumor progression through various mechanisms. Transforming growth factor beta (TGFß)-mediated secretion of Angiopoietin-like 4 (ANGPTL4) is important for cancer development. Here, Formin-like 2 (FMNL2) is identified to be necessary for ANGPTL4 trafficking and secretion in response to TGFß. Protein kinase C (PKC)-dependent phosphorylation of FMNL2 downstream of TGFß stimulation is required for cancer cell invasion as well as ANGPTL4 vesicle trafficking and secretion. Moreover, using super resolution microscopy, ANGPTL4 trafficking is actin-dependent with FMNL2 directly polymerizing actin at ANGPTL4-containing vesicles, which are associated with Rab8a and myosin Vb. This work uncovers a formin-controlled mechanism that transiently polymerizes actin directly at intracellular vesicles to facilitate their mobility. This mechanism may be important for the regulation of cancer cell metastasis and tumor progression.

Filamentous nuclear actin regulation of PML NBs during the DNA damage response is deregulated by prelamin A.

Nuclear actin participates in a continuously expanding list of core processes within eukaryotic nuclei, including the maintenance of genomic integrity. In response to DNA damage, nuclear actin polymerises into filaments that are involved in the repair of damaged DNA through incompletely defined mechanisms. We present data to show that the formation of nuclear F-actin in response to genotoxic stress acts as a scaffold for PML NBs and that these filamentous networks are essential for PML NB fission and recruitment of microbodies to DNA lesions. Further to this, we demonstrate that the accumulation of the toxic lamin A precursor prelamin A induces mislocalisation of nuclear actin to the nuclear envelope and prevents the establishment of nucleoplasmic F-actin networks in response to stress. Consequently, PML NB dynamics and recruitment to DNA lesions is ablated, resulting in impaired DNA damage repair. Inhibition of nuclear export of formin mDia2 restores nuclear F-actin formation by augmenting polymerisation of nuclear actin in response to stress and rescues PML NB localisation to sites of DNA repair, leading to reduced levels of DNA damage.

BCAT1 redox function maintains mitotic fidelity.

The metabolic enzyme branched-chain amino acid transaminase 1 (BCAT1) drives cell proliferation in aggressive cancers such as glioblastoma. Here, we show that BCAT1 localizes to mitotic structures and has a non-metabolic function as a mitotic regulator. Furthermore, BCAT1 is required for chromosome segregation in cancer and induced pluripotent stem cells and tumor growth in human cerebral organoid and mouse syngraft models. Applying gene knockout and rescue strategies, we show that the BCAT1 CXXC redox motif is crucial for controlling cysteine sulfenylation specifically in mitotic cells, promoting Aurora kinase B localization to centromeres, and securing accurate chromosome segregation. These findings offer an explanation for the well-established role of BCAT1 in promoting cancer cell proliferation. In summary, our data establish BCAT1 as a component of the mitotic apparatus that safeguards mitotic fidelity through a moonlighting redox functionality.

The 2020 AIB curriculum survey: The state of internationalizing students, faculty, and programs.

Twenty years after the prior survey, the seventh international business curriculum survey was conducted in 2020 under the sponsorship of the Academy of International Business (AIB) and the Association to Advance Collegiate Schools of Business (AACSB). This paper reports the survey's findings and makes relevant comparisons with the results of the two previous curriculum surveys. This study is not only an update but also explores new directions of international business (IB) integration into the business schools' programs. Although the percentage of matrix structures and separate IB departments is higher in the 2020 survey than earlier, the majority of IB faculty are still scattered across functional departments without IB recognition. Essentially, with few exceptions, we found that European schools are consistently more international than their counterparts elsewhere. Business school deans also consider experiential learning very effective in equipping students with IB knowledge and are generally quite satisfied with the overall progress of their internationalization efforts. The survey findings contribute to understanding how IB is integrated into business schools and offer insights for identifying future opportunities. Supplementary Information: The online version contains supplementary material available at 10.1057/s41267-022-00547-1.

Vingt ans après l'enquête précédente, la septième enquête sur les programmes d'études en affaires internationales a été menée en 2020 sous le parrainage de l'Academy of International Business (AIB) et de l'Association to Advance Collegiate Schools of Business (AACSB). Cet article présente les résultats de l'enquête et établit des comparaisons pertinentes avec les résultats des deux enquêtes précédentes sur les programmes d'études. Cette recherche n'est pas seulement une mise à jour, mais explore également les nouvelles directions de l'intégration des affaires internationales (International Business - IB) dans les programmes des écoles de commerce. Bien que le pourcentage de structures matricielles et de départements distincts de l'IB soit plus élevé dans l'enquête 2020 que précédemment, la majorité des professeurs d'IB sont toujours dispersés dans les départements fonctionnels sans reconnaissance de l'IB. Globalement, à quelques exceptions près, nous constatons que les écoles européennes sont systématiquement plus internationales que leurs homologues ailleurs. Les doyens des écoles de commerce considèrent également que l'apprentissage expérientiel est très efficace pour doter les élèves des connaissances en IB, et sont généralement assez satisfaits de la progression globale de leurs efforts d'internationalisation. Les résultats de l'enquête permettent de mieux comprendre comment l'IB est intégré dans les écoles de commerce et offrent des pistes pour identifier de futures opportunités.

Veinte años después de la encuesta anterior, en 2020 se llevó a cabo la séptima encuesta sobre los planes de estudios de negocios internacionales, CON el patrocinio de la Academia de Negocios Internacionales (AIB) y la Asociación para el Avance de las Escuelas Universitarias de Negocios (AACSB). Este documento reporta los resultados de la encuesta y realiza las comparaciones pertinentes con los resultados de las dos encuestas curriculares anteriores. Este estudio no sólo es una actualización, sino que también explora nuevas direcciones de la integración de los negocios internacionales en los programas de las escuelas de negocios. Aunque el porcentaje de estructuras matriciales y departamentos separados de negocios internacionales es mayor en la encuesta de 2020 que antes, la mayoría del profesorado de negocios internacionales sigue disperso en departamentos funcionales sin reconocimiento de negocios internacionales. Esencialmente, con pocas excepciones, encontramos que las escuelas europeas son sistemáticamente más internacionales que sus homólogas de otros lugares. Los decanos de las escuelas de negocios también consideran que el aprendizaje experimental es muy eficaz para equipar a los estudiantes de conocimientos en negocios internacionales y, en general, están bastante satisfechos con el progreso general de sus esfuerzos de internacionalización. Los resultados de la encuesta contribuyen a entender cómo se integra negocios internacionales en las escuelas de negocios y ofrecen ideas para identificar futuras oportunidades.

Vinte anos após a pesquisa anterior, a sétima pesquisa de currículo de negócios internacionais foi realizada em 2020 sob o patrocínio da Academy of International Business (AIB) e da Association to Advance Collegiate Schools of Business (AACSB). Este artigo relata as descobertas da pesquisa e faz comparações relevantes com os resultados das duas pesquisas curriculares anteriores. Este estudo não é apenas uma atualização, mas também explora novas direções da integração de negócios internacionais (IB) com programas das escolas de negócios. Embora a porcentagem de estruturas matriciais e departamentos de IB distintos seja maior na pesquisa de 2020 do que na anterior, a maioria do corpo docente de IB ainda está espalhada por departamentos funcionais sem reconhecimento de IB. Essencialmente, com poucas exceções, descobrimos que escolas europeias são consistentemente mais internacionais do que suas contrapartes em outros lugares. Reitores de escolas de negócios também consideram o aprendizado experimental muito eficaz para equipar alunos com conhecimento sobre IB e geralmente estão bastante satisfeitos com o progresso geral de seus esforços de internacionalização. Os resultados da pesquisa contribuem para entender como IB está integrado às escolas de negócios e oferecem insights para identificar oportunidades futuras.

Within-host evolution of SARS-CoV-2 in an immunosuppressed COVID-19 patient as a source of immune escape variants.

The origin of SARS-CoV-2 variants of concern remains unclear. Here, we test whether intra-host virus evolution during persistent infections could be a contributing factor by characterizing the long-term SARS-CoV-2 infection dynamics in an immunosuppressed kidney transplant recipient. Applying RT-qPCR and next-generation sequencing (NGS) of sequential respiratory specimens, we identify several mutations in the viral genome late in infection. We demonstrate that a late viral isolate exhibiting genome mutations similar to those found in variants of concern first identified in UK, South Africa, and Brazil, can escape neutralization by COVID-19 antisera. Moreover, infection of susceptible mice with this patient's escape variant elicits protective immunity against re-infection with either the parental virus and the escape variant, as well as high neutralization titers against the alpha and beta SARS-CoV-2 variants, B.1.1.7 and B.1.351, demonstrating a considerable immune control against such variants of concern. Upon lowering immunosuppressive treatment, the patient generated spike-specific neutralizing antibodies and resolved the infection. Our results suggest that immunocompromised patients could be a source for the emergence of potentially harmful SARS-CoV-2 variants.

Yersinia pseudotuberculosis cytotoxic necrotizing factor interacts with glycosaminoglycans.

The Cytotoxic Necrotizing Factor Y (CNFY) is produced by the gram-negative, enteric pathogen Yersinia pseudotuberculosis. The bacterial toxin belongs to a family of deamidases, which constitutively activate Rho GTPases, thereby balancing inflammatory processes. We identified heparan sulfate proteoglycans as essential host cell factors for intoxication with CNFY. Using flow cytometry, microscopy, knockout cell lines, pulsed electron-electron double resonance, and bio-layer interferometry, we studied the role of glucosaminoglycans in the intoxication process of CNFY. Especially the C-terminal part of CNFY, which encompasses the catalytic activity, binds with high affinity to heparan sulfates. CNFY binding with the N-terminal domain to a hypothetical protein receptor may support the interaction between the C-terminal domain and heparan sulfates, which seems sterically hindered in the full toxin. A second conformational change occurs by acidification of the endosome, probably allowing insertion of the hydrophobic regions of the toxin into the endosomal membrane. Our findings suggest that heparan sulfates play a major role for intoxication within the endosome, rather than being relevant for an interaction at the cell surface.

Optogenetic Control of Myocardin-Related Transcription Factor A Subcellular Localization and Transcriptional Activity Steers Membrane Blebbing and Invasive Cancer Cell Motility.

The myocardin-related transcription factor A (MRTF-A) controls the transcriptional activity of the serum response factor (SRF) in a tightly controlled actin-dependent manner. In turn, MRTF-A is crucial for many actin-dependent processes including adhesion, migration, and contractility and has emerged as a novel target for anti-tumor strategies. MRTF-A rapidly shuttles between cytoplasmic and nuclear compartment via dynamic actin interactions within its N-terminal RPEL domain. Here, optogenetics is used to spatiotemporally control MRTF-A nuclear localization by blue light using the light-oxygen-voltage-sensing domain 2-domain based system LEXY (light-inducible nuclear export system). It is found that light-regulated nuclear export of MRTF-A occurs within 10-20 min. Importantly, MRTF-A-LEXY shuttling is independent of perturbations of actin dynamics. Furthermore, light-regulation of MRTF-A-LEXY is reversible and repeatable for several cycles of illumination and its subcellular localization correlates with SRF transcriptional activity. As a consequence, optogenetic control of MRTF-A subcellular localization determines subsequent cytoskeletal dynamics such as non-apoptotic plasma membrane blebbing as well as invasive tumor-cell migration through 3D collagen matrix. This data demonstrates robust optogenetic regulation of MRTF as a powerful tool to control SRF-dependent transcription as well as cell motile behavior.

Characterization of a L136P mutation in Formin-like 2 (FMNL2) from a patient with chronic inflammatory bowel disease.

Diaphanous related formins are highly conserved proteins regulated by Rho-GTPases that act as actin nucleation and assembly factors. Here we report the functional characterization of a non-inherited heterozygous FMNL2 p.L136P mutation carried by a patient who presented with severe very early onset inflammatory bowel disease (IBD). We found that the FMNL2 L136P protein displayed subcellular mislocalization and deregulated protein autoinhibition indicating gain-of-function mechanism. Expression of FMNL2 L136P impaired cell spreading as well as filopodia formation. THP-1 macrophages expressing FMNL2 L136P revealed dysregulated podosome formation and a defect in matrix degradation. Our data indicate that the L136P mutation affects cellular actin dynamics in fibroblasts and immune cells such as macrophages.