Phosphorylation of Nonmuscle myosin II-A regulatory light chain resists Sendai virus fusion with host cells

Monoclonal Antibodies Targeting Porcine Macrophages Are Able to Inhibit the Cell Entry of Macrophage-Tropic Viruses (PRRSV and ASFV)

Porcine reproductive and respiratory syndrome virus (PRRSV) and African swine fever virus (ASFV) cause serious economic losses to the swine industry worldwide. Both viruses show a tropism for macrophages, based on the use of specific entry mediators (e.g., Siglec-1 and CD163). Identifying additional mediators of viral entry is essential for advancing antiviral and vaccine development. In this context, monoclonal antibodies (mAbs) are valuable tools. This study employed a library of 166 mAbs targeting porcine alveolar macrophages (PAMs) to identify candidates capable of blocking early infection stages, including viral binding, internalization, and fusion. Immunofluorescence analysis revealed 74 mAbs with cytoplasmic staining and 70 mAbs with membrane staining. Fifteen reacted with blood monocytes as determined by flow cytometry. mAb blocking assays were performed at 4 °C and 37 °C to analyze the ability of mAbs to block PRRSV and/or ASFV infections in PAMs. The mAb 28C10 significantly blocked PRRSV (96% at 4 °C and 80% at 37 °C) and ASFV (64% at 4 °C and 81% at 37 °C) infections. The mAb 28G10B6 significantly blocked PRRSV (86% at 4 °C and 74% at 37 °C) and partially blocked ASFV (35% at 4 °C and 64% at 37 °C) infections. mAb 26B8F5-I only partially blocked PRRSV infection (65% at 4 °C and 46% at 37 °C). Western blotting and mass spectrometry identified the corresponding proteins as Siglec-1 (28C10; 250 kDa), MYH9 (28G10B6; 260 kDa), and ANXA1 (26B8F5-I; 37 kDa). Our findings are indicative that Siglec-1, MYH9, and ANXA1 play a role in PRRSV/ASFV entry into macrophages.

The actin cytoskeleton is important for pseudorabies virus infection

Viruses are dependent on the host factors for their replication and survival. Therefore, identification of host factors that druggable for antiviral development is crucial. The actin cytoskeleton plays an important role in the virus infection. The dynamics change of actin and its function are regulated by multiple actin-associated proteins (AAPs). However, the role and mechanism of various AAPs in the life cycle of virus are still enigmatic. In this study, we analyzed the roles of actin and AAPs in the replication of pseudorabies virus (PRV). Using a library of compounds targeting AAPs, our data found that multiple AAPs, such as Rho-GTPases, Rock, Myosin and Formin were involved in PRV infection. Besides, our result demonstrated that the actin-binding protein Drebrin was also participated in PRV infection. Further studies are necessary to elucidate the molecular mechanism of AAPs in the virus life cycle, in the hope of mining host factors for antiviral developments.

RhoA suppresses pseudorabies virus replication in vitro

The porcine pseudorabies virus (PRV) is one of the most devastating pathogens and brings great economic losses to the swine industry worldwide. Viruses are intracellular parasites that have evolved numerous strategies to subvert and utilize different host processes for their life cycle. Among the different systems of the host cell, the cytoskeleton is one of the most important which not only facilitate viral invasion and spread into neighboring cells, but also help viruses to evade the host immune system. RhoA is a key regulator of cytoskeleton system that may participate in virus infection. In this study, we characterized the function of RhoA in the PRV replication by chemical drugs treatment, gene knockdown and gene over-expression strategy. Inhibition of RhoA by specific inhibitor and gene knockdown promoted PRV proliferation. On the contrary, overexpression of RhoA or activation of RhoA by chemical drug inhibited PRV infection. Besides, our data demonstrated that PRV infection induced the disruption of actin stress fiber, which was consistent with previous report. In turn, the actin specific inhibitor cytochalasin D markedly disrupted the normal fibrous structure of intracellular actin cytoskeleton and decreased the PRV replication, suggesting that actin cytoskeleton polymerization contributed to PRV replication in vitro. In summary, our data displayed that RhoA was a host restriction factor that inhibited PRV replication, which may deepen our understanding the pathogenesis of PRV and provide further insight into the prevention of PRV infection and the development of anti-viral drugs.

Actomyosin-dependent cell contractility orchestrates Zika virus infection

Emerging pathogen infections, such as Zika virus (ZIKV), pose an increasing threat to human health, but the role of mechanobiological attributes of host cells during ZIKV infection is largely unknown. Here, we reveal that ZIKV infection leads to increased contractility of host cells. Importantly, we investigated whether host cell contractility contributes to ZIKV infection efficacy, from both the intracellular and extracellular perspective. By performing drug perturbation and gene editing experiments, we confirmed that disruption of contractile actomyosin compromises ZIKV infection efficiency, viral genome replication and viral particle production. By culturing on compliant matrix, we further demonstrate that a softer substrate, leading to less contractility of host cells, compromises ZIKV infection, which resembles the effects of disrupting intracellular actomyosin organization. Together, our work provides evidence to support a positive correlation between host cell contractility and ZIKV infection efficacy, thus unveiling an unprecedented layer of interplay between ZIKV and the host cell.

Assembly and disassembly dynamics of nonmuscle myosin II control endosomal fission

Endocytic vesicular trafficking requires merging of two lipid bilayers, but how the two lipid bilayers can come close together during fusion and fission in endocytic trafficking is not well explored. Here, we establish that knocking down nonmuscle myosin IIs (NM IIs) by small interfering RNA (siRNA) or inhibition of their activities by (-) blebbistatin causes the formation of a ring-like assembly of early endosomes (raEE). Inhibition of NM II assembly by an inhibitor of regulatory light-chain (RLC) kinase results in the formation of raEE, whereas inhibition of NM II disassembly by inhibitors of heavy chain kinases, protein kinase C (PKC) and casein kinase 2 (CK2), causes the dispersion of early endosomes. The raEEs retain EEA1, Rab7, and LAMP2 markers. Overexpression of an assembly incompetent form, RLC-AA, and disassembly incompetent form, NMHCIIB-S6A or NMHCIIA-1916A, induces such defects, respectively. Altogether, these data support that NM II assembly and disassembly dynamics participate in endocytic trafficking by regulating fission to maintain the size of early endosomes.

ROCK1/MLC2 inhibition induces decay of viral mRNA in BPXV infected cells

Rho-associated coiled-coil containing protein kinase 1 (ROCK1) intracellular cell signaling pathway regulates cell morphology, polarity, and cytoskeletal remodeling. We observed the activation of ROCK1/myosin light chain (MLC2) signaling pathway in buffalopox virus (BPXV) infected Vero cells. ROCK1 depletion by siRNA and specific small molecule chemical inhibitors (Thiazovivin and Y27632) resulted in a reduced BPXV replication, as evidenced by reductions in viral mRNA/protein synthesis, genome copy numbers and progeny virus particles. Further, we demonstrated that ROCK1 inhibition promotes deadenylation of viral mRNA (mRNA decay), mediated via inhibiting interaction with PABP [(poly(A)-binding protein] and enhancing the expression of CCR4-NOT (a multi-protein complex that plays an important role in deadenylation of mRNA). In addition, ROCK1/MLC2 mediated cell contraction, and perinuclear accumulation of p-MLC2 was shown to positively correlate with viral mRNA/protein synthesis. Finally, it was demonstrated that the long-term sequential passage (P = 50) of BPXV in the presence of Thiazovivin does not select for any drug-resistant virus variants. In conclusion, ROCK1/MLC2 cell signaling pathway facilitates BPXV replication by preventing viral mRNA decay and that the inhibitors targeting this pathway may have novel therapeutic effects against buffalopox.

Myosin motors on the pathway of viral infections

Molecular motors are microscopic machines that use energy from adenosine triphosphate (ATP) hydrolysis to generate movement. While kinesins and dynein are molecular motors associated with microtubule tracks, myosins bind to and move on actin filaments. Mammalian cells express several myosin motors. They power cellular processes such as endo- and exocytosis, intracellular trafficking, transcription, migration, and cytokinesis. As viruses navigate through cells, they may take advantage or be hindered by host components and machinery, including the cytoskeleton. This review delves into myosins' cell roles and compares them to their reported functions in viral infections. In most cases, the previously described myosin functions align with their reported role in viral infections, although not in all cases. This opens the possibility that knowledge obtained from studying myosins in viral infections might shed light on new physiological roles for myosins in cells. However, given the high number of myosins expressed and the variety of viruses investigated in the different studies, it is challenging to infer whether the interactions found are specific to a single virus or can be applied to other viruses with the same characteristics. We conclude that the participation of myosins in viral cycles is still a largely unexplored area, especially concerning unconventional myosins.

How Physical Factors Coordinate Virus Infection: A Perspective From Mechanobiology

Pandemics caused by viruses have threatened lives of thousands of people. Understanding the complicated process of viral infection provides significantly directive implication to epidemic prevention and control. Viral infection is a complex and diverse process, and substantial studies have been complemented in exploring the biochemical and molecular interactions between viruses and hosts. However, the physical microenvironment where infections implement is often less considered, and the role of mechanobiology in viral infection remains elusive. Mechanobiology focuses on sensation, transduction, and response to intracellular and extracellular physical factors by tissues, cells, and extracellular matrix. The intracellular cytoskeleton and mechanosensors have been proven to be extensively involved in the virus life cycle. Furthermore, innovative methods based on micro- and nanofabrication techniques are being utilized to control and modulate the physical and chemical cell microenvironment, and to explore how extracellular factors including stiffness, forces, and topography regulate viral infection. Our current review covers how physical factors in the microenvironment coordinate viral infection. Moreover, we will discuss how this knowledge can be harnessed in future research on cross-fields of mechanobiology and virology.

Stress fiber anisotropy contributes to force-mode dependent chromatin stretching and gene upregulation in living cells

Living cells and tissues experience various complex modes of forces that are important in physiology and disease. However, how different force modes impact gene expression is elusive. Here we apply local forces of different modes via a magnetic bead bound to the integrins on a cell and quantified cell stiffness, chromatin deformation, and DHFR (dihydrofolate reductase) gene transcription. In-plane stresses result in lower cell stiffness than out-of-plane stresses that lead to bead rolling along the cell long axis (i.e., alignment of actin stress fibers) or at different angles (90° or 45°). However, chromatin stretching and ensuing DHFR gene upregulation by the in-plane mode are similar to those induced by the 45° stress mode. Disrupting stress fibers abolishes differences in cell stiffness, chromatin stretching, and DHFR gene upregulation under different force modes and inhibiting myosin II decreases cell stiffness, chromatin deformation, and gene upregulation. Theoretical modeling using discrete anisotropic stress fibers recapitulates experimental results and reveals underlying mechanisms of force-mode dependence. Our findings suggest that forces impact biological responses of living cells such as gene transcription via previously underappreciated means.

Living cells and tissues experience various complex modes of forces but how different force modes impact gene expression is elusive. Here authors apply forces via magnetic beads to integrins on a cell surface and observe force-mode dependent chromatin stretching and gene upregulation in cells and identify underlying mechanisms.

Nonmuscle myosin IIA and IIB differentially modulate migration and alter gene expression in primary mouse tumorigenic cells

Though many cancers are known to show up-regulation of nonmuscle myosin (NM) IIA and IIB, the mechanism by which NMIIs aid in cancer development remains unexplored. Here we demonstrate that tumor-generating, fibroblast-like cells isolated from 3-methylcholanthrene (3MC)-induced murine tumor exhibit distinct phospho-dependent localization of NMIIA and NMIIB at the perinuclear area and tip of the filopodia and affect cell migration differentially. While NMIIA-KD affects protrusion dynamics and increases cell directionality, NMIIB-KD lowers migration speed and increases filopodial branching. Strategically located NMIIs at the perinuclear area colocalize with the linker of nucleoskeleton and cytoskeleton (LINC) protein Nesprin2 and maintain the integrity of the nuclear-actin cap. Interestingly, knockdown of NMIIs results in altered expression of genes involved in epithelial-to-mesenchymal transition, angiogenesis, and cellular senescence. NMIIB-KD cells display down-regulation of Gsc and Serpinb2, which is strikingly similar to Nesprin2-KD cells as assessed by quantitative PCR analysis. Further gene network analysis predicts that NMIIA and NMIIB may act on similar pathways but through different regulators. Concomitantly, knockdown of NMIIA or NMIIB lowers the growth rate and tumor volume of 3MC-induced tumor in vivo. Altogether, these results open a new window to further investigate the effect of LINC-associated perinuclear actomyosin complex on mechanoresponsive gene expression in the growing tumor.

Sendai virus recruits cellular villin to remodel actin cytoskeleton during fusion with hepatocytes

Reconstituted Sendai viral envelopes (virosomes) are well recognized for their promising potential in membrane fusion-mediated delivery of bioactive molecules to liver cells. Despite the known function of viral envelope glycoproteins in catalyzing fusion with cellular membrane, the role of host cell proteins remains elusive. Here, we used two-dimensional differential in-gel electrophoresis to analyze hepatic cells in early response to virosome-induced membrane fusion. Quantitative mass spectrometry together with biochemical analysis revealed that villin, an actin-modifying protein, is differentially up-regulated and phosphorylated at threonine 206-an early molecular event during membrane fusion. We found that villin influences actin dynamics and that this influence, in turn, promotes membrane mixing through active participation of Sendai viral envelope glycoproteins. Modulation of villin in host cells also resulted in a discernible effect on the entry and egress of progeny Sendai virus. Taken together, these results suggest a novel mechanism of regulated viral entry in animal cells mediated by host factor villin.

Gene silencing NMII promotes axonal regeneration against contusive spinal cord injury in rats

There are drastic changes that occur in the impaired regions after spinal cord injury (SCI), however, improvement of the detrimental pathological process after injury is limited in the mammalian adult, which is due a large part to the failure of local axons to grow. Non-muscle myosin II (NMII) has been proved having essential role in the regulation of cytoskeletal structure and genetic silencing NMII markedly accelerates axon growth in vitro. Our purpose is to explore the association between phosphorylated NMII expression and axonal regeneration after SCI in rats and determine whether gene silencing NMII can improve the locomotor function in rats with SCI. The results showed that phosphorylated NMII level was up regulated after SCI and may even play important role in inhibiting neuronal survival and axonal regeneration. After silencing NMII, the viability of neurons, proliferation of axons, synaptic connection and locomotor functional recovery were promoted significantly after SCI. Our study provides an effective way by direct regulation of neuron viability, the proliferation of axons and synaptic connection for treating SCI, which may be a novel method for repairing SCI. However, the specific signaling pathway mechanisms about the recovery require further study.

Fusions of Tumor-derived Endothelial Cells with Dendritic Cells Induces Antitumor Immunity

To explore dendritic cells/tumor-derived endothelial cells (DC/EC) fusion cells are potent stimulators of T cells to impact tumor progression. ECs were isolated from mice hepatoma cell line (H22) Xenograft, and dendritic cells were isolated from bone marrow of BALB/c mice, then the isolated ECs were cultured and detected the endothelial surface expression of CD105 by flow cytometry. The endothelial characteristics of ECs were detected by tube formation assay and Dil-Ac-LDL uptake assay. After the fusion with polyethylene glycol (PEG), we used DCs, ECs, DCs mixed ECs as the control groups, DC/EC fusion cells as the experimental group, Secretion of IFN-α and IFN-γ was evaluated, T lymphocyte proliferation and cytotoxic T lymphocytes (CTL) were detected in vitro. In vivo, T lymphocyte induced by five groups was injected to detect the effect of tumor progression. Purified ECs (CD105⁺) took the function of endothelial cells, then successfully fused with DCs. The DC/EC fusion cells were functional in stimulating the proliferation of T cells, which produced IFN-α and IFN-γ. In vivo, T cells stimulated by DC/EC fusion cells effectively repressed tumor growth. The fusion cells, which was capable of stimulating T cells, is indispensable for antitumor immunity.

MYH9 is an Essential Factor for Porcine Reproductive and Respiratory Syndrome Virus Infection

Porcine reproductive and respiratory syndrome (PRRS) caused by the PRRS virus (PRRSV) is an important swine disease worldwide. PRRSV has a limited tropism for certain cells, which may at least in part be attributed to the expression of the necessary cellular molecules serving as the virus receptors or factors on host cells for virus binding or entry. However, these molecules conferring PRRSV infection have not been fully characterized. Here we show the identification of non-muscle myosin heavy chain 9 (MYH9) as an essential factor for PRRSV infection using the anti-idiotypic antibody specific to the PRRSV glycoprotein GP5. MYH9 physically interacts with the PRRSV GP5 protein via its C-terminal domain and confers susceptibility of cells to PRRSV infection. These findings indicate that MYH9 is an essential factor for PRRSV infection and provide new insights into PRRSV-host interactions and viral entry, potentially facilitating development of control strategies for this important swine disease.