Search Results (110)

The nuclear membrane has emerged as a dynamic regulatory platform coordinating genome organization, mechanotransduction, and regulated cell death (RCD). Beyond its barrier function, the nuclear skeleton—comprising lamins, actin–myosin isoforms, nuclear matrix proteins, and the LINC complex—supports nuclear integrity and gene regulation. Recent evidence shows that type II membrane-bound bZIP transcription factors such as cAMP-responsive element-binding protein 3 (CREB3) and CREB3L1 localize to the inner nuclear membrane (INM), linking chromatin tethering with stress signaling. Their stress-induced cleavage by S1P/S2P disrupts chromatin anchoring and, in some contexts, triggers karyoptosis, a novel form of RCD defined by nuclear rupture. These findings position the nuclear envelope (NE) as a mechanosensitive signaling hub with direct implications for disease and therapy. In this review, we provide a comprehensive discussion on how type II membrane-bound bZIP transcription factors and chromatin acting as a nucleoskeleton cooperate to regulate nuclear membrane integrity. Full article

The SARS-CoV-2 spike protein, through its receptor binding domain (S1-RBD), binds to the angiotensin-converting enzyme 2 (ACE2) receptor on the host cell membrane, leading to viral infection. Several mutations in S1-RBD in SARS-CoV-2 variants are known to enhance infection through an increased affinity for ACE2. While many reports are available describing the SARS-CoV-2 infection mechanism, there is a dearth of studies towards understanding the initial interaction of the S1-RBD with ACE2 on living host cells and the role of endocytosis and cytoskeleton in the process. Here, we reconstituted the interaction between S1-RBD- and ACE2-expressing host cells in a hybrid live cell-supported lipid bilayer (SLB) platform enabling live monitoring of the interaction between S1-RBD on SLBs and the ACE2 receptor on living cells and showed that cells depleted Omicron S1-RBD from SLB corrals, likely through endocytosis. Specifically, interaction of living host cells with S1-RBD-functionalized SLB substrates resulted in the enrichment of S1-RBD and ACE2 at the cell–SLB interface. Interaction of host cells with wild type (WT), Omicron, and Omicron Revertant S1-RBD functionalized on micron-scale SLB corrals, which mimic viral membranes but are flat, also resulted in their enrichment. However, cells interacting with Omicron S1-RBD revealed a depletion of the protein from many corrals, which was generally not observed with the WT S1-RBD and was reduced with the Omicron Revertant, which contains the Q493R mutation reversion, S1-RBD. Further, S1-RBD depletion coincided with the localization of the early endosomal marker EEA1. Importantly, treatment of cells with the clathrin inhibitor, pitstop 2, but not the myosin II inhibitor, blebbistatin, significantly reduced Omicron S1-RBD depletion. Collectively, these observations suggest that the SARS-CoV-2 Omicron variant has evolved, through mutations in its S1-RBD, to take advantage of the cellular endocytic pathway for enhanced infection, which is not observed with the parental SARS-CoV-2 and appears to be lost in the Omicron Revertant variant. Additionally, these results underscore the significance of the hybrid live cell–SLB platform in studying SARS-CoV-2 S1-RBD-ACE2 interaction and the potential impact of mutations in the S1-RBD on adapting to a specific cellular entry mechanism. Full article

Duck enteritis virus (DEV) is responsible for duck viral enteritis, a contagious and lethal disease in waterfowls. The host proteins targeted by DEV are unknown. In this study, we developed a recombinant DEV rVP26-Flag and identified 17 host proteins that interact with VP26 in infected chicken embryo fibroblast cells using co-immunoprecipitation in conjunction with liquid chromatography–tandem mass spectrometry (Co-IP-MS/MS). The 17 potential targets of VP26 proteins include Xirp1, TMOD3, DCN, ATP5PD, AP3M1, MYO5A, MYH10, MYH9 (non-muscle myosin IIA heavy chain), and GSN. Most of these proteins are microfilament or cytoskeletal proteins with functions such as cytoskeletal protein binding, actin filament interaction, microfilament motor activity, and myosin II interaction. Using the Search Tool for the Retrieval of Interacting Genes analysis, we predicted a functional network of microfilament cytoskeletal proteins interacting with VP26. Interaction between DEV VP26 and the carboxyl-terminus domain of MYH9 (1651–1960 aa) was verified via co-localization and Co-IP assays. We also demonstrated that the inhibition of actin polymerization with cytochalasin D and latrunculin A reduced the DEV titer. Furthermore, siRNA-mediated knockdown of MYH9, which has intrinsic ATPase activity, also resulted in a reduced viral titer. A targeted inhibitor of myosin II ATPase, (-)-Blebbistatin, significantly suppressed DEV infection both in vitro and in vivo. These results suggest that the actin–myosin II network plays a crucial role in DEV proliferation, with MYH9 being an important host factor influencing DEV infection. Full article

Focal adhesions (FAs) are multi-protein complexes that mediate cell attachment to the extracellular matrix. Their formation and maturation depend on intracellular tension generated by actin filaments interacting with phosphorylated myosin II. Using live-cell and confocal microscopy, we investigated how FA dynamics are regulated by actin polymerization and myosin II-driven contractility. We found that knockdown of myosin II resulted in complete and irreversible disassembly of FAs. However, partial inhibition of myosin II, through either ROCK or myosin light chain kinase (MLCK) inhibitors, leads to gradual FA shrinkage. In contrast, complete inhibition of myosin II phosphorylation causes disassembly of existing FAs, followed by the formation of new, small FAs at the cell periphery. In both cases, FAs formed after inhibition of myosin II phosphorylation exhibited significantly longer lifespans than FAs in control cells. Similarly, partial inhibition of actin polymerization using nanomolar concentrations of latrunculin B or cytochalasin D also promoted the formation of small FAs. Complete and irreversible FA disassembly occurred only when actin filaments were fully disrupted, leading to cell lamella retraction. These findings suggest that actin polymerization at the cell edge is the minimal and sufficient requirement for the assembly of small FAs. Notably, our data demonstrate for the first time that perturbation of the actin–myosin system results in stabilization and prolonged lifespan of small FAs, whereas larger FAs, formed in the presence of myosin II activity, are more dynamic. Together, these results emphasize the essential role of cortical actin organization and myosin II phosphorylation in the maintenance and turnover of FAs. Full article

Background: The candidate therapeutic peptide TnP demonstrates broad, system-level regulatory capacity, revealed through integrated network analysis from transcriptomic data in zebrafish. Our study primarily identifies TnP as a multifaceted modulator of drug metabolism, wound healing, proteolytic activity, and pigmentation pathways. Results: Transcriptomic profiling of TnP-treated larvae following tail fin amputation revealed 558 differentially expressed genes (DEGs), categorized into four functional networks: (1) drug-metabolizing enzymes (cyp3a65, cyp1a) and transporters (SLC/ABC families), where TnP alters xenobiotic processing through Phase I/II modulation; (2) cellular trafficking and immune regulation, with upregulated myosin genes (myhb/mylz3) enhancing wound repair and tlr5-cdc42 signaling fine-tuning inflammation; (3) proteolytic cascades (c6ast4, prss1) coupled to autophagy (ulk1a, atg2a) and metabolic rewiring (g6pca.1-tg axis); and (4) melanogenesis-circadian networks (pmela/dct-fbxl3l) linked to ubiquitin-mediated protein turnover. Key findings highlight TnP’s unique coordination of rapid (protease activation) and sustained (metabolic adaptation) responses, enabled by short network path lengths (1.6–2.1 edges). Hub genes, such as nr1i2 (pxr), ppara, and bcl6aa/b, mediate crosstalk between these systems, while potential risks—including muscle hypercontractility (myhb overexpression) or cardiovascular effects (ace2-ppp3ccb)—underscore the need for targeted delivery. The zebrafish model validated TnP-conserved mechanisms with human relevance, particularly in drug metabolism and tissue repair. TnP’s ability to synchronize extracellular matrix remodeling, immune resolution, and metabolic homeostasis supports its development for the treatment of fibrosis, metabolic disorders, and inflammatory conditions. Conclusions: Future work should focus on optimizing tissue-specific delivery and assessing genetic variability to advance clinical translation. This system-level analysis positions TnP as a model example for next-generation multi-pathway therapeutics. Full article

Skeletal muscle changes occur in heart failure (HF). Despite the cardioprotective effects of sodium–glucose co-transporter 2 (SGLT2) inhibitors in HF, their impact on skeletal muscle remains poorly understood. We investigated the effects of the SGLT2 inhibitor empagliflozin (EMPA) on cardiac remodeling and the soleus muscle of rats with myocardial infarction (MI)-induced HF. Methods: One week after MI induction, rats were assigned to Sham, Sham + EMPA, MI, and MI + EMPA groups. EMPA was administered (5 mg/kg/day) for 12 weeks. Results: MI + EMPA and MI had dilated left cardiac chambers; the left atrium diameter and left ventricle end-diastolic area were smaller in MI + EMPA than MI. The ejection fraction did not differ between infarcted groups. MI + EMPA had a larger soleus cross-sectional area and higher Type II myosin heavy chain expression than MI. Carbonylated protein and malondialdehyde levels were lower and superoxide dismutase activity higher in MI + EMPA than MI. Respiratory Complex I expression was higher in MI + EMPA than MI. Metabolic enzyme activities, altered in MI, were normalized in MI + EMPA. EMPA up-regulated anabolic proteins and down-regulated catabolic proteins. Conclusion: Empagliflozin attenuates infarction-induced cardiac remodeling in rats. In soleus muscle, empagliflozin preserves cell trophism, reduces oxidative stress, normalizes muscle and mitochondrial metabolism, and positively modulates proteins involved in synthesis and degradation-related pathways. Full article

(1) Background: Prompt acute coronary syndrome (ACS) recognition remains challenging. This study evaluated the diagnostic and prognostic performance of novel biomarkers for non-ST-elevation myocardial infarction (NSTEMI). (2) Methods: Patients with suspected ACS presenting to Heidelberg University Hospital’s Emergency Department between August 2014 and February 2023 were analyzed. The biomarker panel included high-sensitivity cardiac troponin T (hs-cTnT), cardiac myosin-binding protein C (cMyBP-C), pro-B-type natriuretic peptide (proBNP), total N-terminal pro-B-type natriuretic peptide (t-NtproBNP), Angiotensin II (Ang2), Bone morphogenetic protein 10 (BMP10), Endothelial cell-specific molecule 1 (ESM1), fatty acid-binding protein 3 (FABP3), Fibroblast growth factor 23 (FGF23), Growth differentiation factor 15 (GDF15), and Copeptin. Negative predictive values (NPVs), sensitivities, and area under the curve (AUC) values were calculated for NSTEMI discrimination. Effectiveness and prognostic performance were assessed based on cardiovascular events at 30 days and 1 year. (3) Results: Of 1765 patients, 212 (12%) were diagnosed with NSTEMI. The European Society of Cardiology (ESC) 0/1 h and 0/3 h algorithms achieved sensitivities of 100% and 96.8%, NPVs of 100% and 99.3%, and effectiveness values of 54.8% and 66.0%. Hs-cTnT (AUC: 0.922) and cMyBP-C (AUC: 0.917) exhibited the highest diagnostic accuracy, followed by FABP3 (AUC: 0.759) and Copeptin (AUC: 0.624). Other biomarkers had lower performance (AUC: 0.516–0.617). At 1 year, event rates ranged from 0.0% to 3.4%, with the ESC algorithms demonstrating superior prognostic performance (0.8%, 2.4%). (4) Conclusions: The ESC 0/1 h and 0/3 h algorithms remain the most effective NSTEMI diagnostic strategies, balancing high sensitivity, prognostic reliability, and effectiveness. Among novel biomarkers, only cMyBP-C demonstrated comparable accuracy to hs-cTnT, supporting its potential as an adjunct to troponin assays. Full article

Multipotent vascular stem cells (MVSCs) are found in the vascular wall and surrounding tissues and possess the ability to differentiate into mesenchymal lineages. Previous studies have shown that MVSCs can be activated in response to vascular injury and differentiate into vascular smooth muscle cells (SMCs), contributing to vascular remodeling and microvessel formation. However, it remains unclear as to whether and how microenvironmental changes in the extracellular matrix, such as substrate stiffness, modulates MVSC differentiation under pathological conditions. This study demonstrated that MVSCs cultured on stiff substrates exhibited increased cell spreading, stronger cell adhesion, and a higher expression of SMC markers, including myosin heavy chain (MHC), myocardin (MYCD), calponin 1 (CNN1), and smooth muscle α-actin (SMA). In contrast, MVSCs on soft substrates showed an elevated expression of the chondrogenic markers aggrecan 1 (AGC1) and collagen-II (COL2A1). The presence of TGF-β1 further increased the expression of SMC markers on stiff substrates and chondrogenic markers on the soft substrates. Collectively, these results establish substrate stiffness as a key regulator of MVSC lineage commitment through cytoskeletal reorganization, with TGF-β1 acting as a biochemical amplifier. Our findings highlight the substrate-stiffness-dependent differentiation of MVSCs and provide mechanistic insights into the role of MVSCs in vascular remodeling during atherosclerosis development and blood vessel regeneration. Full article

Class II myosin (myosin-2) is an actin-based motor protein found in nearly all eukaryotes. One critical question is how the motor function of myosin-2 is regulated. Vertebrate myosin-2 comprises non-muscle myosin, smooth muscle myosin and striated muscle myosin. Recent studies have shown that smooth muscle myosin, in its inhibited state, adopts a folded conformation in which the two heads interact with each other asymmetrically, and the tail is folded into three segments that wrap around the two heads. It has been proposed that the asymmetric head-to-head interaction is a conserved, fundamental structure essential for the regulation of all types of myosin-2. Nearly all insects have only a single striated muscle myosin heavy chain (MHC) gene, which produces all MHC isoforms through alternative splicing of mutually exclusive exons. Most of the alternative exon-encoded regions in insect MHC are located in the motor domain and are critical for generating isoform-specific contraction velocity and force production. However, it remains unclear whether these alternative exon-encoded regions participate in the regulation of insect striated muscle myosin. Here, we review the recently resolved structure of the inhibited state of smooth muscle myosin and discuss its implications on the regulation of insect striated muscle myosin. We propose that the alternative exon-encoded regions in insect MHC not only affect motor properties but also contribute to stabilizing the folded conformation and play a crucial role in regulating insect striated muscle myosin. Full article

Injured or atrophied adult skeletal muscles are regenerated through terminal differentiation of satellite cells to form multinucleated muscle fibers. Transplantation of satellite cells or cultured myoblasts has been used to improve skeletal muscle regeneration. Some of the limitations observed result from the limited number of available satellite cells that can be harvested and the efficiency of fusion of cultured myoblasts with mature muscle fibers (i.e., terminal differentiation) upon transplantation. However, the possible use of immature myotubes in the middle of the terminal differentiation process instead of satellite cells or cultured myoblasts has not been thoroughly investigated. Herein, myoblasts (Mb) or immature myotubes on differentiation day 2 (D2 immature myotubes) or 3 (D3 immature myotubes) were transferred to plates containing D2 or D3 immature myotubes as host cells. The transferred Mb/immature myotubes on the plates were further co-differentiated with host immature myotubes into mature myotubes in six conditions: Mb-to-D2, D2-to-D2, D3-to-D2, Mb-to-D3, D2-to-D3, and D3-to-D3. Among these six co-differentiation conditions, the D2-to-D3 co-differentiation condition exhibited the most characteristic myotube appearance and the greatest availability of Ca²⁺ for skeletal muscle contraction. Compared with non-co-differentiated control myotubes, D2-to-D3 co-differentiated myotubes presented increased MyoD and myosin heavy chain II (MyHC II) expression and increased myotube width, accompanied by parallel and swirling alignment. These increases correlated with functional increases in both electrically induced intracellular Ca²⁺ release and extracellular Ca²⁺ entry due to the increased expression of ryanodine receptor 1 (RyR1), sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase 1a (SERCA1a), and stromal interaction molecule 1 (STIM1). These increases were not detected in any of the other co-differentiation conditions. These results suggest that in vitro-cultured D2-to-D3 co-differentiated mature myotubes could be a good alternative source of satellite cells or cultured myoblasts for skeletal muscle regeneration. Full article

The mammalian Apolipoprotein-L families (APOLs) contain several isoforms of membrane-interacting proteins, some of which are involved in the control of membrane dynamics (traffic, fission and fusion). Specifically, human APOL1 and APOL3 appear to control membrane remodeling linked to pathogen infection. Through its association with Non-Muscular Myosin-2A (NM2A), APOL1 controls Golgi-derived trafficking of vesicles carrying the lipid scramblase Autophagy-9A (ATG9A). These vesicles deliver APOL3 together with phosphatidylinositol-4-kinase-B (PI4KB) and activated Stimulator of Interferon Genes (STING) to mitochondrion–endoplasmic reticulum (ER) contact sites (MERCSs) for the induction and completion of mitophagy and apoptosis. Through direct interactions with PI4KB and PI4KB activity controllers (Neuronal Calcium Sensor-1, or NCS1, Calneuron-1, or CALN1, and ADP-Ribosylation Factor-1, or ARF1), APOL3 controls PI(4)P synthesis. PI(4)P is required for different processes linked to infection-induced inflammation: (i) STING activation at the Golgi and subsequent lysosomal degradation for inflammation termination; (ii) mitochondrion fission at MERCSs for induction of mitophagy and apoptosis; and (iii) phagolysosome formation for antigen processing. In addition, APOL3 governs mitophagosome fusion with endolysosomes for mitophagy completion, and the APOL3-like murine APOL7C is involved in phagosome permeabilization linked to antigen cross-presentation in dendritic cells. Similarly, APOL3 can induce the fusion of intracellular bacterial membranes, and a role in membrane fusion can also be proposed for endothelial APOLd1 and adipocyte mAPOL6, which promote angiogenesis and adipogenesis, respectively, under inflammatory conditions. Thus, different APOL isoforms play distinct roles in membrane remodeling associated with inflammation. Full article

The myosin light chains (MLCs) of non-muscle myosin II are known to regulate cellular architecture and generate cellular forces; they also have an increasingly emerging role in the progression of cancer. The phosphorylation state of the myosin light chains controls the activity of myosins that are implicated in invasion and proliferation. In cancers, when proliferation is greatly increased, cytokinesis relies on phosphorylated light chains to activate the contractile forces used to separate the cells. Likewise, during metastasis, kinase pathways culminate in aligning MLC structures for enhanced cell motility through stress fiber contraction and the accumulation of myosin filaments at the leading edge. This review summarizes the myosin light chain family members known to promote cancer progression and evidence of how their altered activities change the behavior of cells involving the mechanical-based processes of proliferation and cell movements during metastasis. In addition, myosin light chains impact the immune response to cancers and currently serve as biomarkers in staging this disease; a brief summary of these topics is provided at the end of the review. Full article

Non-muscle myosin IIA (NM IIA) is a motor protein that belongs to the myosin II family. The myosin heavy chain 9 (MYH9) gene encodes the heavy chain of NM IIA. NM IIA is a hexamer and contains three pairs of peptides, which include the dimer of heavy chains, essential light chains, and regulatory light chains. NM IIA is a part of the actomyosin complex that generates mechanical force and tension to carry out essential cellular functions, including adhesion, cytokinesis, migration, and the maintenance of cell shape and polarity. These functions are regulated via light and heavy chain phosphorylation at different amino acid residues. Apart from physiological functions, NM IIA is also linked to the development of cancer and genetic and neurological disorders. MYH9 gene mutations result in the development of several autosomal dominant disorders, such as May-Hegglin anomaly (MHA) and Epstein syndrome (EPS). Multiple studies have reported NM IIA as a tumor suppressor in melanoma and head and neck squamous cell carcinoma; however, studies also indicate that NM IIA is a critical player in promoting tumorigenesis, chemoradiotherapy resistance, and stemness. The ROCK-NM IIA pathway regulates cellular movement and shape via the control of cytoskeletal dynamics. In addition, the ROCK-NM IIA pathway is dysregulated in various solid tumors and leukemia. Currently, there are very few compounds targeting NM IIA, and most of these compounds are still being studied in preclinical models. This review provides comprehensive evidence highlighting the dual role of NM IIA in multiple cancer types and summarizes the signaling networks involved in tumorigenesis. Furthermore, we also discuss the role of NM IIA as a potential therapeutic target with a focus on the ROCK-NM IIA pathway. Full article

Background: A major issue in Chronic Myeloid Leukemia (CML) is the persistence of quiescent leukemia stem cells (LSCs) in the hematopoietic niche under tyrosine kinase inhibitor (TKI) treatment. Results: Here, using CFSE sorting, we show that low-proliferating CD34+ cells from CML patients in 3D co-culture hide under HS27A stromal cells during TKI treatment—a behavior less observed in untreated cells. Under the same conditions, Ba/F3p210 cells lose their spontaneous motility. In CML CD34+ and Ba/F3p210 cells, while Rac1 is completely inhibited by TKI, RhoA remains activated but is unable to signal to ROCK. Co-incubation of Ba/F3p210 cells with TKI, SKF-96365 (a calcium channel inhibitor), and EGF restores myosin II activation and amoeboid motility to levels comparable to untreated cells, sustaining the activation of ROCK. In CFSE+ CD34+ cells containing quiescent leukemic stem cells, co-incubation of TKI with SKF-96365 induced the expulsion of these cells from the HS27A niche. Conclusions: This study underscores the role of RhoA in LSC behavior under TKI treatment and suggests that SKF-96365 could remobilize quiescent CML LSCs through reactivation of the RhoA/ROCK pathway. Full article

Cytokinesis, the last step in cell division, separates daughter cells through mechanical force. This is often through the force produced by an actomyosin contractile ring. In fission yeast cells, the ring helps recruit a mechanosensitive ion channel, Pkd2, to the cleavage furrow, whose activation by membrane tension promotes calcium influx and daughter cell separation. However, it is unclear how the activities of Pkd2 may affect the actomyosin ring. Here, through both microscopic and genetic analyses of a hypomorphic pkd2 mutant, we examined the potential role of this essential gene in assembling the contractile ring. The pkd2-81KD mutation significantly increased the counts of the type II myosin heavy chain Myo2 (+18%), its regulatory light chain Rlc1 (+37%) and actin (+100%) molecules in the ring, compared to the wild type. Consistent with a regulatory role of Pkd2 in the ring assembly, we identified a strong negative genetic interaction between pkd2-81KD and the temperature-sensitive mutant myo2-E1. The pkd2-81KD myo2-E1 cells often failed to assemble a complete contractile ring. We conclude that Pkd2 modulates the recruitment of type II myosin and actin to the contractile ring, suggesting a novel calcium-dependent mechanism regulating the actin cytoskeletal structures during cytokinesis. Full article