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.

Spatio-Temporal Regulation of RhoGTPases Signaling by Myosin II

RhoGTPase activation of non-muscle myosin II regulates cell division, extrusion, adhesion, migration, and tissue morphogenesis. However, the regulation of myosin II and mechanotransduction is not straightforward. Increasingly, the role of myosin II on the feedback regulation of RhoGTPase signaling is emerging. Indeed, myosin II controls RhoGTPase signaling through multiple mechanisms, namely contractility driven advection, scaffolding, and sequestration of signaling molecules. Here we discuss these mechanisms by which myosin II regulates RhoGTPase signaling in cell adhesion, migration, and tissue morphogenesis.

Herpesvirus acts with the cytoskeleton and promotes cancer progression

The cytoskeleton is a complex fibrous reticular structure composed of microfilaments, microtubules and intermediate filaments. These components coordinate morphology support and intracellular transport that is involved in a variety of cell activities, such as cell proliferation, migration and differentiation. In addition, the cytoskeleton also plays an important role in viral infection. During an infection by a Herpesvirus, the virus utilizes microfilaments to enter cells and travel to the nucleus by microtubules; the viral DNA replicates with the help of host microfilaments; and the virus particles start assembling with a capsid in the cytoplasm before egress. The cytoskeleton changes in cells infected with Herpesvirus are made to either counteract or obey the virus, thereby promote cell transforming into cancerous ones. This article aims to clarify the interaction between the virus and cytoskeleton components in the process of Herpesvirus infection and the molecular motor, cytoskeleton-associated proteins and drugs that play an important role in the process of a Herpesvirus infection and carcinogenesis process.

Mechanical Durotactic Environment Enhances Specific Glioblastoma Cell Responses

Background: A hallmark of glioblastoma is represented by their ability to widely disperse throughout the brain parenchyma. The importance of developing new anti-migratory targets is critical to reduce recurrence and improve therapeutic efficacy. Methods: Polydimethylsiloxane substrates, either mechanically uniform or presenting durotactic cues, were fabricated to assess GBM cell morphological and dynamical response with and without pharmacological inhibition of NNMII contractility, of its upstream regulator ROCK and actin polymerization. Results: Glioma cells mechanotactic efficiency varied depending on the rigidity compliance of substrates. Morphologically, glioma cells on highly rigid and soft bulk substrates displayed bigger and elongated aggregates whereas on durotactic substrates the same cells were homogeneously dispersed with a less elongated morphology. The durotactic cues also induced a motility change, cell phenotype dependent, and with cells being more invasive on stiffer substrates. Pharmacological inhibition of myosin or ROCK revealed a rigidity-insensitivity, unlike inhibition of microfilament contraction and polymerization of F-actin, suggesting that alternative signalling is used to respond to durotactic cues. Conclusions: The presence of a distinct mechanical cue is an important factor in cell migration. Together, our results provide support for a durotactic role of glioma cells that acts through actomyosin contractility to regulate the aggressive properties of GBM cells.

Non-muscle Myosin II: Role in Microbial Infection and Its Potential as a Therapeutic Target

Currently, the major measures of preventing and controlling microbial infection are vaccinations and drugs. However, the appearance of drug resistance microbial mounts is main obstacle in current anti-microbial therapy. One of the most ubiquitous actin-binding proteins, non-muscle myosin II (NM II) plays a crucial role in a wide range of cellular physiological activities in mammals, including cell adhesion, migration, and division. Nowadays, growing evidence indicates that aberrant expression or activity of NM II can be detected in many diseases caused by microbes, including viruses and bacteria. Furthermore, an important role for NM II in the infection of some microbes is verified. Importantly, modulating the expression of NM II with small hairpin RNA (shRNA) or the activity of it by inhibitors can affect microbial-triggered phenotypes. Therefore, NM II holds the promise to be a potential target for inhibiting the infection of microbes and even treating microbial-triggered discords. In spite of these, a comprehensive view on the functions of NM II in microbial infection and the regulators which have an impact on the roles of NM II in this context, is still lacking. In this review, we summarize our current knowledge on the roles of NM II in microbial-triggered discords and provide broad insights into its regulators. In addition, the existing challenge of investigating the multiple roles of NM II in microbial infection and developing NM II inhibitors for treating these microbial-triggered discords, are also discussed.

MYH9 Promotes Growth and Metastasis via Activation of MAPK/AKT Signaling in Colorectal Cancer

The contractile protein MYH9 (non-muscle myosin IIA) is an actin-binding protein that plays a fundamental role in cell adhesion, migration, and division. However, its distinct role in colorectal cancer (CRC) still remains unidentified. In this study, we detected significant MYH9 overexpression in CRC samples compared with paired normal tissues using western blotting and tissue microarray immunohistochemistry (IHC). Moreover, analysis of patient clinical information demonstrated that MYH9 overexpression was strongly correlated with lymph node metastasis and poor overall survival. Endogenous overexpression of MYH9 enhanced the ability of cell proliferation and migration in vitro, and accelerated CRC growth in mouse models. Silencing of MYH9 revealed repressive effects on CRC cells in vitro and in vivo. Furthermore, primary biomechanics that involved MAPK/AKT signaling mediated epithelial-mesenchymal transition (EMT) was uncovered underlying MYH9 dependent cell behaviors. Collectively, our data showed that MYH9 significantly promoted tumorigenesis by regulating MAPK/AKT signaling, and was remarkably correlated with poor prognosis in CRC. MYH9 may thus be a novel biomarker and drug target in the diagnosis and treatment of CRC.

The actomyosin network is influenced by NMHC IIA and regulated by CrpF46, which is involved in controlling cell migration

When a cell migrates, the centrosome positions between the nucleus and the leading edge of migration via the microtubule system. The protein Crp^F46 (centrosome-related protein F46) has a known role during mitosis and centrosome duplication. However, how Crp^F46 efficiently regulates centrosome-related cell migration is unclear. Here, we report that knockdown of Crp^F46 resulted in the disruption of microtubule arrangement, with impaired centrosomal reorientation, and slowed down cell migration. In cells that express low levels of Crp^F46, stress fibers were weakened, which could be rescued by recovering Flag-Crp^F46. We also found that Crp^F46 interacted with non-muscle myosin high chain IIA (NMHC IIA) and that its three coiled-coil domains are pivotal for its binding to NMHC IIA. Additionally, analyses of phosphorylation of NMHC IIA and RLC (regulatory light chain) demonstrated that Crp^F46 was associated with myosin IIA during filament formation. Indirect immunofluorescence images indicated that NM IIA filaments were inhibited when Crp^F46 was under-expressed. Thus, Crp^F46 regulates cell migration by centrosomal reorientation and altering the function of the actomyosin network by controlling specific phosphorylation of myosin.

Myosin Heavy Chain 10 (MYH10) Gene Silencing Reduces Cell Migration and Invasion in the Glioma Cell Lines U251, T98G, and SHG44 by Inhibiting the Wnt/β-Catenin Pathway

Background

The myosin heavy chain 10 or MYH10 gene encodes non-muscle myosin II B (NM IIB), and is involved in tumor cell migration, invasion, extracellular matrix (ECM) production, and epithelial-mesenchymal transition (EMT). This study aimed to investigate the effects of the MYH10 gene on normal human glial cells and glioma cell lines in vitro, by gene silencing, and to determine the signaling pathways involved.

Material/Methods

The normal human glial cell line HEB, and the glioma cell lines, U251, T98G, and SHG44 were studied. Plasmid transfection silenced the MYH10 gene. The cell counting kit-8 (CCK-8) assay evaluated cell viability. Cell migration and invasion were evaluated using scratch and transwell assays. Western blot measured the protein expression levels, and quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the mRNA expression levels, for MYH10, metastasis-associated protein 1 (MTA-1), matrix metalloproteinase (MMP)-1, MMP-9, tissue inhibitor of metalloproteinases 2 (TIMP2), collagen 1, E-cadherin, vimentin, Wnt3a, β-catenin, and cyclin D1.

Results

The MYH10 gene was overexpressed in U251, T98G, and SHG44 cells. MYH10 expression was down-regulated following siMYH10 plasmid interference, which also inhibited glioma cell migration and invasion. MYH10 gene silencing resulted in reduced expression of MTA-1, MPP-2, MMP-9 and vimentin, and increased expression of TIMP-2, E-cadherin and collagen 1 at the protein and mRNA level, and inhibited the Wnt/β-catenin pathway.

Conclusions

In human glioma cell lines, silencing the MYH10 gene reduced cell migration and invasion, by inhibiting the Wnt/β-catenin pathway, which may regulate the ECM and inhibit EMT in human glioma.

Myh10 deficiency leads to defective extracellular matrix remodeling and pulmonary disease

Impaired alveolar formation and maintenance are features of many pulmonary diseases that are associated with significant morbidity and mortality. In a forward genetic screen for modulators of mouse lung development, we identified the non-muscle myosin II heavy chain gene, Myh10. Myh10 mutant pups exhibit cyanosis and respiratory distress, and die shortly after birth from differentiation defects in alveolar epithelium and mesenchyme. From omics analyses and follow up studies, we find decreased Thrombospondin expression accompanied with increased matrix metalloproteinase activity in both mutant lungs and cultured mutant fibroblasts, as well as disrupted extracellular matrix (ECM) remodeling. Loss of Myh10 specifically in mesenchymal cells results in ECM deposition defects and alveolar simplification. Notably, MYH10 expression is downregulated in the lung of emphysema patients. Altogether, our findings reveal critical roles for Myh10 in alveologenesis at least in part via the regulation of ECM remodeling, which may contribute to the pathogenesis of emphysema.

N-terminal acetylation and methylation differentially affect the function of MYL9

Deciphering the histone code has illustrated that acetylation or methylation on the same residue can have analogous or opposing roles. However, little is known about the interplay between these post-translational modifications (PTMs) on the same nonhistone residues. We have recently discovered that N-terminal acetyltransferases (NATs) and N-terminal methyltransferases (NRMTs) can have overlapping substrates and identified myosin regulatory light chain 9 (MYL9) as the first confirmed protein to occur in either α-amino-methylated (Nα-methyl) or α-amino-acetylated (Nα-acetyl) states in vivo Here we aim to determine if these PTMs function similarly or create different MYL9 proteoforms with distinct roles. We use enzymatic assays to directly verify MYL9 is a substrate of both NRMT1 and NatA and generate mutants of MYL9 that are exclusive for Nα-acetylation or Nα-methylation. We then employ eukaryotic cell models to probe the regulatory functions of these Nα-PTMs on MYL9. Our results show that, contrary to prevailing dogma, neither of these modifications regulate the stability of MYL9. Rather, exclusive Nα-acetylation promotes cytoplasmic roles of MYL9, while exclusive Nα-methylation promotes the nuclear role of MYL9 as a transcription factor. The increased cytoplasmic activity of Nα-acetylated MYL9 corresponds with increased phosphorylation at serine 19, a key MYL9 activating PTM. Increased nuclear activity of Nα-methylated MYL9 corresponds with increased DNA binding. Nα-methylation also results in a decrease of interactions between the N-terminus of MYL9 and a host of cytoskeletal proteins. These results confirm that Nα-acetylation and Nα-methylation differentially affect MYL9 function by creating distinct proteoforms with different internal PTM patterns and binding properties.

Blebbistatin modulates prostatic cell growth and contrapctility through myosin II signaling

To investigate the effect of blebbistatin (BLEB, a selective myosin inhibitor) on regulating contractility and growth of prostate cells and to provide insight into possible mechanisms associated with these actions. BLEB was incubated with cell lines of BPH-1 and WPMY-1, and intraprostatically injected into rats. Cell growth was determined by flow cytometry, and in vitro organ bath studies were performed to explore muscle contractility. Smooth muscle (SM) myosin isoform (SM1/2, SM-A/B, and LC_17a/b) expression was determined via competitive reverse transcriptase PCR. SM myosin heavy chain (MHC), non-muscle (NM) MHC isoforms (NMMHC-A and NMMHC-B), and proteins related to cell apoptosis were further analyzed via Western blotting. Masson's trichrome staining was applied to tissue sections. BLEB could dose-dependently trigger apoptosis and retard the growth of BPH-1 and WPMY-1. Consistent with in vitro effect, administration of BLEB to the prostate could decrease rat prostatic epithelial and SM cells via increased apoptosis. Western blotting confirmed the effects of BLEB on inducing apoptosis through a mechanism involving MLC₂₀ dephosphorylation with down-regulation of Bcl-2 and up-regulation of BAX and cleaved caspase 3. Meanwhile, NMMHC-A and NMMHC-B, the downstream proteins of MLC₂₀, were found significantly attenuated in BPH-1 and WPMY-1 cells, as well as rat prostate tissues. Additionally, BLEB decreased SM cell number and SM MHC expression, along with attenuated phenylephrine-induced contraction and altered prostate SMM isoform composition with up-regulation of SM-B and down-regulation of LC_17a, favoring a faster contraction. Our novel data demonstrate BLEB regulated myosin expression and functional activity. The mechanism involved MLC₂₀ dephosphorylation and altered SMM isoform composition.

ALPK1 Expression Is Associated with Lymph Node Metastasis and Tumor Growth in Oral Squamous Cell Carcinoma Patients

Oral squamous cell carcinoma (OSCC) is the most common malignant cancer, with high mortality rates in advanced stages. Recent studies have shown that the expression of ALPK1 mRNA and its inhibitory differentiation function are associated with cancer progression. However, the expression and clinicopathologic features of ALPK1 in OSCC remain unexplored. Herein, the authors investigated the expression patterns of ALPK1 in 39 matched OSCC patients and examined the relationship between ALPK1 protein expression and clinicopathologic factors using immunohistochemical scores. Using Western blot analysis, ALPK1 expression was found to be significantly higher in tumor tissues than that in nontumor tissues. Through an immunoreactive scoring system, a significantly higher number of advanced-stage tumor size T4 and lymph node metastasis N2 exhibited higher ALPK1 expression levels than that exhibited by T1/T2/T3 tumors and N0/N1. In addition, ALPK1 protein expression was aberrant in malignant oral cancer cell lines compared with that in pre-malignant oral epithelial cells, whereas minimal expression was observed in normal oral epithelial cells. Knockdown of ALPK1 resulted in a significant reduction in cell growth, migration, and invasion capacity in vitro. Consequently, expression of N-cadherin and vimentin decreased in ALPK1-deficient cells. Thus, these results suggest that ALPK1 serves as a potential biomarker and target for OSCC development in late stages.

Myosin-IIA heavy chain phosphorylation on S1943 regulates tumor metastasis

Nonmuscle myosin-IIA (NMHC-IIA) heavy chain phosphorylation has gained recognition as an important feature of myosin-II regulation. In previous work, we showed that phosphorylation on S1943 promotes myosin-IIA filament disassembly in vitro and enhances EGF-stimulated lamellipod extension of breast tumor cells. However, the contribution of NMHC-IIA S1943 phosphorylation to the modulation of invasive cellular behavior and metastasis has not been examined. Stable expression of phosphomimetic (S1943E) or non-phosphorylatable (S1943A) NMHC-IIA in breast cancer cells revealed that S1943 phosphorylation enhances invadopodia function, and is critical for matrix degradation in vitro and experimental metastasis in vivo. These studies demonstrate a novel link between NMHC-IIA S1943 phosphorylation, the regulation of extracellular matrix degradation and tumor cell invasion and metastasis.

A Genetically Encoded Biosensor Strategy for Quantifying Non-muscle Myosin II Phosphorylation Dynamics in Living Cells and Organisms

Complex cell behaviors require dynamic control over non-muscle myosin II (NMMII) regulatory light chain (RLC) phosphorylation. Here, we report that RLC phosphorylation can be tracked in living cells and organisms using a homotransfer fluorescence resonance energy transfer (FRET) approach. Fluorescent protein-tagged RLCs exhibit FRET in the dephosphorylated conformation, permitting identification and quantification of RLC phosphorylation in living cells. This approach is versatile and can accommodate several different fluorescent protein colors, thus enabling multiplexed imaging with complementary biosensors. In fibroblasts, dynamic myosin phosphorylation was observed at the leading edge of migrating cells and retracting structures where it persistently colocalized with activated myosin light chain kinase. Changes in myosin phosphorylation during C. elegans embryonic development were tracked using polarization inverted selective-plane illumination microscopy (piSPIM), revealing a shift in phosphorylated myosin localization to a longitudinal orientation following the onset of twitching. Quantitative analyses further suggested that RLC phosphorylation dynamics occur independently from changes in protein expression.

Medicinal Chemistry and Use of Myosin II Inhibitor ( S)-Blebbistatin and Its Derivatives

( S)-Blebbistatin, a chiral tetrahydropyrroloquinolinone, is a widely used and well-characterized ATPase inhibitor selective for myosin II. The central role of myosin II in many normal and pathological biological processes has been revealed with the aid of this small molecule. The first part of this manuscript provides a summary of myosin II and ( S)-blebbistatin literature from a medicinal chemist's perspective. The second part of this perspective deals with the physicochemical deficiencies that trouble the use of ( S)-blebbistatin in advanced biological settings: low potency and solubility, fluorescence interference, (photo)toxicity, and stability issues. A large toolbox of analogues has been developed in which particular shortcomings have been addressed. This perspective provides a necessary overview of these developments and presents guidelines for selecting the best available analogue for a given application. As the unmet need for high-potency analogues remains, we also propose starting points for medicinal chemists in search of nanomolar myosin II inhibitors.

Self-organized stress patterns drive state transitions in actin cortices

Biological functions rely on ordered structures and intricately controlled collective dynamics. This order in living systems is typically established and sustained by continuous dissipation of energy. The emergence of collective patterns of motion is unique to nonequilibrium systems and is a manifestation of dynamic steady states. Mechanical resilience of animal cells is largely controlled by the actomyosin cortex. The cortex provides stability but is, at the same time, highly adaptable due to rapid turnover of its components. Dynamic functions involve regulated transitions between different steady states of the cortex. We find that model actomyosin cortices, constructed to maintain turnover, self-organize into distinct nonequilibrium steady states when we vary cross-link density. The feedback between actin network structure and organization of stress-generating myosin motors defines the symmetries of the dynamic steady states. A marginally cross-linked state displays divergence-free long-range flow patterns. Higher cross-link density causes structural symmetry breaking, resulting in a stationary converging flow pattern. We track the flow patterns in the model actomyosin cortices using fluorescent single-walled carbon nanotubes as novel probes. The self-organization of stress patterns we have observed in a model system can have direct implications for biological functions.

Substrate deformations induce directed keratinocyte migration

Cell migration is an essential part of many (patho)physiological processes, including keratinocyte re-epithelialization of healing wounds. Physical forces and mechanical cues from the wound bed (in addition to biochemical signals) may also play an important role in the healing process. Previously, we explored this possibility and found that polyacrylamide (PA) gel stiffness affected human keratinocyte behaviour and that mechanical deformations in soft (approx. 1.2 kPa) PA gels produced by neighbouring cells appeared to influence the process of de novo epithelial sheet formation. To clearly demonstrate that keratinocytes do respond to such deformations, we conducted a series of experiments where we observed the response of single keratinocytes to a prescribed local substrate deformation that mimicked a neighbouring cell or evolving multicellular aggregate via a servo-controlled microneedle. We also examined the effect of adding either Y27632 or blebbistatin on cell response. Our results indicate that keratinocytes do sense and respond to mechanical signals comparable to those that originate from substrate deformations imposed by neighbouring cells, a finding that could have important implications for the process of keratinocyte re-epithelialization that takes place during wound healing. Furthermore, the Rho/ROCK pathway and the engagement of NM II are both essential to substrate deformation-directed keratinocyte migration.

Slow calcium waves mediate furrow microtubule reorganization and germ plasm compaction in the early zebrafish embryo

Zebrafish germ plasm ribonucleoparticles (RNPs) become recruited to furrows of early zebrafish embryos through their association with astral microtubules ends. During the initiation of cytokinesis, microtubules are remodeled into a furrow microtubule array (FMA), which is thought to be analogous to the mammalian midbody involved in membrane abscission. During furrow maturation, RNPs and FMA tubules transition from their original distribution along the furrow to enrichments at the furrow distal ends, which facilitates germ plasm mass compaction. We show that nebel mutants exhibit reduced furrow-associated slow calcium waves (SCWs), caused at least in part by defective enrichment of calcium stores. RNP and FMA distal enrichment mirrors the medial-to-distal polarity of SCWs, and inhibition of calcium release or downstream mediators such as Calmodulin affects RNP and FMA distal enrichment. Blastomeres with reduced or lacking SCWs, such as early blastomeres in nebel mutants and wild-type blastomeres at later stages, exhibit medially bundling microtubules similar to midbodies in other cell types. Our data indicate that SCWs provide medial-to-distal directionality along the furrow to facilitate germ plasm RNP enrichment at the furrow ends.

Nonmuscle myosin IIA is involved in recruitment of apical junction components through activation of α-catenin

MDCK dog kidney epithelial cells express two isoforms of nonmuscle myosin heavy chain II, IIA and IIB. Using the CRISPR/Cas9 system, we established cells in which the IIA gene was ablated. These cells were then transfected with a vector that expresses GFP-IIA chimeric molecule under the control of a tetracycline-responsible element. In the absence of Dox (doxycyclin), when GFP-IIA is expressed (GFP-IIA+), the cells exhibit epithelial cell morphology, but in the presence of Dox, when expression of GFP-IIA is repressed (GFP-IIA-), the cells lose epithelial morphology and strong cell-cell adhesion. Consistent with these observations, GFP-IIA- cells failed to assemble junction components such as E-cadherin, desmoplakin, and occludin at cell-cell contact sites. Therefore, IIA is required for assembly of junction complexes. MDCK cells with an ablation of the α-catenin gene also exhibited the same phenotype. However, when in GFP-IIA- cells expressed α-catenin lacking the inhibitory region or E-cadherin/α-catenin chimeras, the cells acquired the ability to establish the junction complex. These experiments reveal that IIA acts as an activator of α-catenin in junction assembly.

A comprehensive comparison of four species of Onchidiidae provides insights on the morphological and molecular adaptations of invertebrates from shallow seas to wetlands

The Onchidiidae family is ideal for studying the evolution of marine invertebrate species from sea to wetland environments. However, comparative studies of Onchidiidae species are rare. A total of 40 samples were collected from four species (10 specimens per onchidiid), and their histological and molecular differences were systematically evaluated to elucidate the morphological foundations underlying the adaptations of these species. A histological analysis was performed to compare the structures of respiratory organs (gill, lung sac, dorsal skin) among onchidiids, and transcriptome sequencing of four representative onchidiids was performed to investigate the molecular mechanisms associated with their respective habitats. Twenty-six SNP markers of Onchidium reevesii revealed some DNA polymorphisms determining visible traits. Non-muscle myosin heavy chain II (NMHC II) and myosin heavy chain (MyHC), which play essential roles in amphibian developmental processes, were found to be differentially expressed in different onchidiids and tissues. The species with higher terrestrial ability and increased integrated expression of Os-MHC (NMHC II gene) and the MyHC gene, illustrating that the expression levels of these genes were associated with the evolutionary degree. This study provides a comprehensive analysis of the adaptions of a diverse and widespread group of invertebrates, the Onchidiidae. Some onchidiids can breathe well through gills and skin when under seawater, and some can breathe well through lung sacs and skin when in wetlands. A histological comparison of respiratory organs and the relative expression levels of two genes provided insights into the adaptions of onchidiids that allowed their transition from shallow seas to wetlands. This work provides a valuable reference and might encourage further study.

Different contributions of nonmuscle myosin IIA and IIB to the organization of stress fiber subtypes in fibroblasts

We demonstrated that myosin IIA and IIB are essential for the formation of transverse arcs and ventral stress fibers, respectively. Furthermore, we illustrated the roles of both isoforms in lamellar flattening and also raised the possibility that actin filaments in ventral stress fibers are in a stretched conformation.

The myosin light-chain kinase MLCK-1 relocalizes during Caenorhabditis elegans ovulation to promote actomyosin bundle assembly and drive contraction

We identify the Caenorhabditis elegans myosin light-chain kinase, MLCK-1, required for contraction of spermathecae. During contraction, MLCK-1 moves from the apical cell boundaries to the basal actomyosin bundles, where it stabilizes myosin downstream of calcium signaling. MLCK and ROCK act in distinct subsets of cells to coordinate the timing of contraction.

Myosin IIA interacts with the spectrin-actin membrane skeleton to control red blood cell membrane curvature and deformability

The biconcave disk shape and deformability of mammalian RBCs rely on the membrane skeleton, a viscoelastic network of short, membrane-associated actin filaments (F-actin) cross-linked by long, flexible spectrin tetramers. Nonmuscle myosin II (NMII) motors exert force on diverse F-actin networks to control cell shapes, but a function for NMII contractility in the 2D spectrin-F-actin network of RBCs has not been tested. Here, we show that RBCs contain membrane skeleton-associated NMIIA puncta, identified as bipolar filaments by superresolution fluorescence microscopy. MgATP disrupts NMIIA association with the membrane skeleton, consistent with NMIIA motor domains binding to membrane skeleton F-actin and contributing to membrane mechanical properties. In addition, the phosphorylation of the RBC NMIIA heavy and light chains in vivo indicates active regulation of NMIIA motor activity and filament assembly, while reduced heavy chain phosphorylation of membrane skeleton-associated NMIIA indicates assembly of stable filaments at the membrane. Treatment of RBCs with blebbistatin, an inhibitor of NMII motor activity, decreases the number of NMIIA filaments associated with the membrane and enhances local, nanoscale membrane oscillations, suggesting decreased membrane tension. Blebbistatin-treated RBCs also exhibit elongated shapes, loss of membrane curvature, and enhanced deformability, indicating a role for NMIIA contractility in promoting membrane stiffness and maintaining RBC biconcave disk cell shape. As structures similar to the RBC membrane skeleton exist in many metazoan cell types, these data demonstrate a general function for NMII in controlling specialized membrane morphology and mechanical properties through contractile interactions with short F-actin in spectrin-F-actin networks.

Myosins as fundamental components during tumorigenesis: diverse and indispensable

Myosin is a kind of actin-based motor protein. As the crucial functions of myosin during tumorigenesis have become increasingly apparent, the profile of myosin in the field of cancer research has also been growing. Eighteen distinct classes of myosins have been discovered in the past twenty years and constitute a diverse superfamily. Various myosins share similar structures. They all convert energy from ATP hydrolysis to exert mechanical stress upon interactions with microfilaments. Ongoing research is increasingly suggesting that at least seven kinds of myosins participate in the formation and development of cancer. Myosins play essential roles in cytokinesis failure, chromosomal and centrosomal amplification, multipolar spindle formation and DNA microsatellite instability. These are all prerequisites of tumor formation. Subsequently, myosins activate various processes of tumor invasion and metastasis development including cell migration, adhesion, protrusion formation, loss of cell polarity and suppression of apoptosis. In this review, we summarize the current understanding of the roles of myosins during tumorigenesis and discuss the factors and mechanisms which may regulate myosins in tumor progression. Furthermore, we put forward a completely new concept of “chromomyosin” to demonstrate the pivotal functions of myosins during karyokinesis and how this acts to optimize the functions of the members of the myosin superfamily.

A PH-like domain of the Rab12 guanine nucleotide exchange factor DENND3 binds actin and is required for autophagy

Rab GTPases are key regulators of membrane trafficking, and many are activated by guanine nucleotide exchange factors bearing a differentially expressed in normal and neoplastic cells (DENN) domain. By activating the small GTPase Rab12, DENN domain-containing protein 3 (DENND3) functions in autophagy. Here, we identified a structural domain (which we name PHenn) containing a pleckstrin homology subdomain that binds actin and is required for DENND3 function in autophagy. We found that a hydrophobic patch on an extended β-turn of the PHenn domain mediates an intramolecular interaction with the DENN domain of DENND3. We also show that DENND3 binds actin through a surface of positively charged residues on the PHenn domain. Substitutions that blocked either DENN or actin binding compromised the role of DENND3 in autophagy. These results provide new mechanistic insight into the structural determinants regulating DENND3 in autophagy and lay the foundation for future investigations of the DENN protein family.

Proteomic investigation of the effects of preimplantation factor on human embryo implantation

Despite the use of adjuvant therapies, the cumulative proportion of live births remains at ~40%. Accumulating data show that low pregnancy rates, even in the presence of high fertility rates, are due to implantation failure. The present study aimed to identify and construct a profile of proteins that react with preimplantation factor (PIF) and to provide an understanding into the molecular mechanisms by which PIF promotes trophoblast invasion. Cytoplasmic proteins were immunoprecipitated with biotin-labeled synthetic PIF or intralipid and scrambled PIF (PIFscr). The protein profiles were analyzed using isobaric tags for relative and absolute quantification coupled with mass spectrometry. Immunoprecipitation and western blot analyses were used to assess the interactions between PIF and myosin heavy chain 10 (MYH10) and heat shock protein family D1. Small interfering RNA-based silencing was performed to examine the function of MYH10. In the results of the present study, 21 proteins were identified with interactions with PIF. The immunoprecipitation and western blot analyses revealed an interaction between PIF and MYH10. Silencing of the expression of MYH10 in HEC-1-B cells significantly attenuated cell migration and invasion capacities. These data support the conclusion that MYH10-mediated cell migration and invasion act in conjunction with PIF to promote the trophoblast invasion procedure.

Thermodynamic Aspects and Reprogramming Cellular Energy Metabolism during the Fibrosis Process

Fibrosis is characterized by fibroblast proliferation and fibroblast differentiation into myofibroblasts, which generate a relaxation-free contraction mechanism associated with excessive collagen synthesis in the extracellular matrix, which promotes irreversible tissue retraction evolving towards fibrosis. From a thermodynamic point of view, the mechanisms leading to fibrosis are irreversible processes that can occur through changing the entropy production rate. The thermodynamic behaviors of metabolic enzymes involved in fibrosis are modified by the dysregulation of both transforming growth factor β (TGF-β) signaling and the canonical WNT/β-catenin pathway, leading to aerobic glycolysis, called the Warburg effect. Molecular signaling pathways leading to fibrosis are considered dissipative structures that exchange energy or matter with their environment far from the thermodynamic equilibrium. The myofibroblastic cells arise from exergonic processes by switching the core metabolism from oxidative phosphorylation to glycolysis, which generates energy and reprograms cellular energy metabolism to induce the process of myofibroblast differentiation. Circadian rhythms are far-from-equilibrium thermodynamic processes. They directly participate in regulating the TGF-β and WNT/β-catenin pathways involved in energetic dysregulation and enabling fibrosis. The present review focusses on the thermodynamic implications of the reprogramming of cellular energy metabolism, leading to fibroblast differentiation into myofibroblasts through the positive interplay between TGF-β and WNT/β-catenin pathways underlying in fibrosis.

Non-muscle myosin IIB (Myh10) is required for epicardial function and coronary vessel formation during mammalian development

The coronary vasculature is an essential vessel network providing the blood supply to the heart. Disruptions in coronary blood flow contribute to cardiac disease, a major cause of premature death worldwide. The generation of treatments for cardiovascular disease will be aided by a deeper understanding of the developmental processes that underpin coronary vessel formation. From an ENU mutagenesis screen, we have isolated a mouse mutant displaying embryonic hydrocephalus and cardiac defects (EHC). Positional cloning and candidate gene analysis revealed that the EHC phenotype results from a point mutation in a splice donor site of the Myh10 gene, which encodes NMHC IIB. Complementation testing confirmed that the Myh10 mutation causes the EHC phenotype. Characterisation of the EHC cardiac defects revealed abnormalities in myocardial development, consistent with observations from previously generated NMHC IIB null mouse lines. Analysis of the EHC mutant hearts also identified defects in the formation of the coronary vasculature. We attribute the coronary vessel abnormalities to defective epicardial cell function, as the EHC epicardium displays an abnormal cell morphology, reduced capacity to undergo epithelial-mesenchymal transition (EMT), and impaired migration of epicardial-derived cells (EPDCs) into the myocardium. Our studies on the EHC mutant demonstrate a requirement for NMHC IIB in epicardial function and coronary vessel formation, highlighting the importance of this protein in cardiac development and ultimately, embryonic survival.

Interactions between TGF-β1, canonical WNT/β-catenin pathway and PPAR γ in radiation-induced fibrosis

Radiation therapy induces DNA damage and inflammation leading to fibrosis. Fibrosis can occur 4 to 12 months after radiation therapy. This process worsens with time and years. Radiation-induced fibrosis is characterized by fibroblasts proliferation, myofibroblast differentiation, and synthesis of collagen, proteoglycans and extracellular matrix. Myofibroblasts are non-muscle cells that can contract and relax. Myofibroblasts evolve towards irreversible retraction during fibrosis process. In this review, we discussed the interplays between transforming growth factor-β1 (TGF-β1), canonical WNT/β-catenin pathway and peroxisome proliferator-activated receptor gamma (PPAR γ) in regulating the molecular mechanisms underlying the radiation-induced fibrosis, and the potential role of PPAR γ agonists. Overexpression of TGF-β and canonical WNT/β-catenin pathway stimulate fibroblasts accumulation and myofibroblast differentiation whereas PPAR γ expression decreases due to the opposite interplay of canonical WNT/β-catenin pathway. Both TGF-β1 and canonical WNT/β-catenin pathway stimulate each other through the Smad pathway and non-Smad pathways such as phosphatidylinositol 3-kinase/serine/threonine kinase (PI3K/Akt) signaling. WNT/β-catenin pathway and PPAR γ interact in an opposite manner. PPAR γ agonists decrease β-catenin levels through activation of inhibitors of the WNT pathway such as Smad7, glycogen synthase kinase-3 (GSK-3 β) and dickkopf-related protein 1 (DKK1). PPAR γ agonists also stimulate phosphatase and tensin homolog (PTEN) expression, which decreases both TGF-β1 and PI3K/Akt pathways. PPAR γ agonists by activating Smad7 decrease Smads pathway and then TGF-β signaling leading to decrease radiation-induced fibrosis. TGF-β1 and canonical WNT/β-catenin pathway promote radiation-induced fibrosis whereas PPAR γ agonists can prevent radiation-induced fibrosis.

The saponin D39 blocks dissociation of non-muscular myosin heavy chain IIA from TNF receptor 2, suppressing tissue factor expression and venous thrombosis

BACKGROUND AND PURPOSE

Non-muscular myosin heavy chain IIA (NMMHC IIA) plays a key role in tissue factor expression and venous thrombosis. Natural products might inhibit thrombosis through effects on NMMHC IIA. Here, we have shown that a natural saponin, D39, from Liriope muscari exerted anti-thrombotic activity in vivo, by targeting NMMHC IIA.

EXPERIMENTAL APPROACH

Expression and activity of tissue factor in endothelial cells were analysed in vitro by Western blot and simplified chromogenic assays. Interactions between D39 and NMMHC IIA were assessed by serial affinity chromatography and molecular docking analysis. D39-dependent interactions between NMMHC IIA and TNF receptor 2 (TNFR2) were measured by immunofluorescence, co-immunoprecipitation and proximity ligation assays. Anti-thrombotic activity of D39 in vivo was evaluated with a model of inferior vena cava ligation injury in mice.

KEY RESULTS

D39 inhibited tissue factor expression and procoagulant activities in HUVECs and decreased thrombus weight in inferior vena cava-ligated mice dose-dependently. Serial affinity chromatography and molecular docking analysis suggested that D39 bound to NMMHC IIA. In HEK293T cells, D39 inhibited tissue factor expression evoked by NMMHC IIA overexpression. This effect was blocked by NMMHC IIA knockdown in HUVECs. D39 inhibited dissociation of NMMHC IIA from TNFR2, which subsequently modulated the Akt/GSK3β-NF-κB signalling pathways.

CONCLUSIONS AND IMPLICATIONS

D39 inhibited tissue factor expression and thrombus formation by modulating the Akt/GSK3β and NF-κB signalling pathways through NMMHC IIA. We identified a new natural product that targeted NMMHC IIA, as a potential treatment for thrombotic disorders and other vasculopathies.

Polarized Distribution of Active Myosin II Regulates Directional Migration of Cultured Olfactory Ensheathing Cells

Migration of olfactory ensheathing cells (OECs) is critical for development of olfactory system and essential for neural regeneration after OEC transplantation into nerve injury site. However, the molecular mechanisms underlying the regulation of directional migration of OECs remain unclear. In this study, we found that in migrating OECs, phosphorylated myosin light chain (p-MLC, active myosin II) displayed a polarized distribution, with the leading front exhibiting higher than soma and trailing process. Over-expression of GFP-MLC significantly reduced OEC migration. Moreover, decreasing this front-to-rear difference of myosin II activity by the frontal application of a ML-7 (myosin II inhibitors) gradient induced the collapse of leading front and reversed soma translocation of OECs, whereas, increasing this front-to-rear difference of myosin II activity by the rear application of a ML-7 or BDM gradient or the frontal application of a Caly (myosin II activator) gradient accelerated the soma translocation of OECs. Finally, myosin II as a downstream signaling of repulsive factor Slit-2 mediated the reversal of soma translocation induced by Slit-2. Taken together, these results suggest that the polarized distribution of active myosin II regulates the directional migration of OECs during spontaneous migration or upon to extracellular stimulation such as Slit-2.

A Rab3a-dependent complex essential for lysosome positioning and plasma membrane repair

Encarnação et al. show that Rab3a, together with its newly identified effector NMHC IIA, mediates the positioning of peripheral lysosomes in nonsecretory cells, thereby promoting lysosome exocytosis and plasma membrane repair.

Lysosome exocytosis plays a major role in resealing plasma membrane (PM) disruptions. This process involves two sequential steps. First, lysosomes are recruited to the periphery of the cell and then fuse with the damaged PM. However, the trafficking molecular machinery involved in lysosome exocytosis and PM repair (PMR) is poorly understood. We performed a systematic screen of the human Rab family to identify Rabs required for lysosome exocytosis and PMR. Rab3a, which partially localizes to peripheral lysosomes, was one of the most robust hits. Silencing of Rab3a or its effector, synaptotagmin-like protein 4a (Slp4-a), leads to the collapse of lysosomes to the perinuclear region and inhibition of PMR. Importantly, we have also identified a new Rab3 effector, nonmuscle myosin heavy chain IIA, as part of the complex formed by Rab3a and Slp4-a that is responsible for lysosome positioning at the cell periphery and lysosome exocytosis.

Non-muscle myosin II deletion in the developing kidney causes ureter-bladder misconnection and apical extrusion of the nephric duct lineage epithelia

In kidney development, connection of the nephric duct (ND) to the cloaca and subsequent sprouting of the ureteric bud (UB) from the ND are important for urinary exit tract formation. Although the roles of Ret signaling are well established, it remains unclear how intracellular cytoskeletal proteins regulate these morphogenetic processes. Myh9 and Myh10 encode two different non-muscle myosin II heavy chains, and Myh9 mutations in humans are implicated in congenital kidney diseases. Here we report that ND/UB lineage-specific deletion of Myh9/Myh10 in mice caused severe hydroureter/hydronephrosis at birth. At mid-gestation, the mutant ND/UB epithelia exhibited aberrant basal protrusion and ectopic UB formation, which likely led to misconnection of the ureter to the bladder. In addition, the mutant epithelia exhibited apical extrusion followed by massive apoptosis in the lumen, which could be explained by reduced apical constriction and intercellular adhesion mediated by E-cadherin. These phenotypes were not ameliorated by genetic reduction of the tyrosine kinase receptor Ret. In contrast, ERK was activated in the mutant cells and its chemical inhibition partially ameliorated the phenotypes. Thus, myosin II is essential for maintaining the apicobasal integrity of the developing kidney epithelia independently of Ret signaling.

Myosin IIA Heavy Chain Phosphorylation Mediates Adhesion Maturation and Protrusion in Three Dimensions

Non-muscle myosin II (NMII) is a conserved force-producing cytoskeletal enzyme with important but poorly understood roles in cell migration. To investigate myosin heavy chain (MHC) phosphorylation roles in 3D migration, we expressed GFP-tagged NMIIA wild-type or mutant constructs in cells depleted of endogenous NMIIA protein. We find that individual mutation or double mutation of Ser-1916 or Ser-1943 to alanine potently blocks recruitment of GFP-NM-IIA filaments to leading edge protrusions in 2D, and this in turn blocks maturation of anterior focal adhesions. When placed in 3D collagen gels, cells expressing wild-type GFP MHC-IIA behave like parental cells, displaying robust and active formation and retraction of protrusions. However, cells depleted of NMIIA or cells expressing the mutant GFP MHC-IIA display severe defects in invasion and in stabilizing protrusions in 3D. These studies reveal an NMIIA-specific role in 3D invasion that requires competence for NMIIA phosphorylation at Ser-1916 and Ser-1943. In sum, these results demonstrate a critical and previously unrecognized role for NMIIA phosphorylation in 3D invasion.

MYH9 binds to lncRNA gene PTCSC2 and regulates FOXE1 in the 9q22 thyroid cancer risk locus

A locus on chromosome 9q22 harbors a SNP (rs965513) firmly associated with risk of papillary thyroid carcinoma (PTC). The locus also comprises the forkhead box E1 (FOXE1) gene, which is implicated in thyroid development, and a long noncoding RNA (lncRNA) gene, papillary thyroid cancer susceptibility candidate 2 (PTCSC2). How these might interact is not known. Here we report that PTCSC2 binds myosin-9 (MYH9). In a bidirectional promoter shared by FOXE1 and PTCSC2, MYH9 inhibits the promoter activity in both directions. This inhibition can be reversed by PTCSC2, which acts as a suppressor. RNA knockdown of FOXE1 in primary thyroid cells profoundly interferes with the p53 pathway. We propose that the interaction between the lncRNA, its binding protein MYH9, and the coding gene FOXE1 underlies the predisposition to PTC triggered by rs965513.

Viruses That Exploit Actin-Based Motility for Their Replication and Spread

The actin cytoskeleton is a crucial part of the eukaryotic cell. Viruses depend on host cells for their replication, and, as a result, many have developed ways of manipulating the actin network to promote their spread. This chapter reviews the various ways in which viruses utilize the actin cytoskeleton at discrete steps in their life cycle, from entry into the host cell, replication, and assembly of new progeny to virus release. Various actin inhibitors that function in different ways to affect proper actin dynamics can be used to parse the role of actin at these steps.

Mammalian Nonmuscle Myosin II Binds to Anionic Phospholipids with Concomitant Dissociation of the Regulatory Light Chain

Mammalian cells express three Class II nonmuscle myosins (NM): NM2A, NM2B, and NM2C. The three NM2s have well established essential roles in cell motility, adhesion, and cytokinesis and less well defined roles in vesicle transport and other processes that would require association of NM2s with cell membranes. Previous evidence for the mechanism of NM2-membrane association includes direct interaction of NM2s with membrane lipids and indirect interaction by association of NM2s with membrane-bound F-actin or peripheral membrane proteins. Direct binding of NM2s to phosphatidylserine-liposomes, but not to phosphatidylcholine-liposomes, has been reported, but the molecular basis of the interaction between NM2s and acidic phospholipids has not been previously investigated. We now show that filamentous, full-length NM2A, NM2B, and NM2C and monomeric, non-filamentous heavy meromyosin bind to liposomes containing one or more acidic phospholipids (phosphatidylserine, phosphatidylinositol 4,5-diphosphate, and phosphatidylinositol 3,4,5-triphosphate) but do not bind to 100% phosphatidylcholine-liposomes. Binding of NM2s to acidic liposomes occurs predominantly through interaction of the liposomes with the regulatory light chain (RLC) binding site in the myosin heavy chain with concomitant dissociation of the RLC. Phosphorylation of myosin-bound RLC by myosin light chain kinase substantially inhibits binding to liposomes of both filamentous NM2 and non-filamentous heavy meromyosin; the addition of excess unbound RLC, but not excess unbound essential light chain, competes with liposome binding. Consistent with the in vitro data, we show that endogenous and expressed NM2A associates with the plasma membrane of HeLa cells and fibrosarcoma cells independently of F-actin.

Coronin 1B supports RhoA signaling at cell-cell junctions through Myosin II

Non-muscle myosin II (NMII) motor proteins are responsible for generating contractile forces inside eukaryotic cells. There is also a growing interest in the capacity for these motor proteins to influence cell signaling through scaffolding, especially in the context of RhoA GTPase signaling. We previously showed that NMIIA accumulation and stability within specific regions of the cell cortex, such as the zonula adherens (ZA), allows the formation of a stable RhoA signaling zone. Now we demonstrate a key role for Coronin 1B in maintaining this junctional pool of NMIIA, as depletion of Coronin 1B significantly compromised myosin accumulation and stability at junctions. The loss of junctional NMIIA, upon Coronin 1B knockdown, perturbed RhoA signaling due to enhanced junctional recruitment of the RhoA antagonist, p190B Rho GAP. This effect was blocked by the expression of phosphomimetic MRLC-DD, thus reinforcing the central role of NMII in regulating RhoA signaling.

Nanowire Magnetoscope Reveals a Cellular Torque with Left-Right Bias

Cellular force regulates many types of cell mechanics and the associated physiological behaviors. Recent evidence suggested that cell motion with left-right (LR) bias may be the origin of LR asymmetry in tissue architecture. As actomyosin activity was found essential in the process, it predicts a type of cellular force that coordinates the development of LR asymmetry in tissue formation. However, due to the lack of appropriate platform, cellular force with LR bias has not yet been found. Here we report a nanowire magnetoscope that reveals a rotating force-torque-exerted by cells. Ferromagnetic nanowires were deposited and internalized by micropatterned cells. Within a uniform, horizontal magnetic field, the nanowires that initially aligned with the magnetic field were subsequently rotated due to the cellular torque. We found that the torque is LR-biased depending on cell types. While NIH 3T3 fibroblasts and human vascular endothelial cells exhibited counterclockwise torque, C2C12 myoblasts showed torque with slight clockwise bias. Moreover, an actin ring composed of transverse arcs and radial fibers was identified as a major factor determining the LR bias of cellular torque, since the disruption of actin ring by biochemical inhibitors or elongated cell shape abrogated the counterclockwise bias of NIH 3T3 fibroblasts. Our finding reveals a LR-biased torque of single cells and a fundamental origin of cytoskeletal chirality. More broadly, we anticipate that our method will provide a different perspective on mechanics-related cell physiology and force transmission necessary for LR propagation in tissue formation.

Substrate Stiffness Regulates the Development of Left-Right Asymmetry in Cell Orientation

Left-right (LR) asymmetry of tissue/organ structure is a morphological feature essential for many tissue functions. The ability to incorporate the LR formation in constructing tissue/organ replacement is important for recapturing the inherent tissue structure and functions. However, how LR asymmetry is formed remains largely underdetermined, which creates significant hurdles to reproduce and regulate the formation of LR asymmetry in an engineering context. Here, we report substrate rigidity functioning as an effective switch that turns on the development of LR asymmetry. Using micropatterned cell-adherent stripes on rigid substrates, we found that cells collectively oriented at a LR-biased angle relative to the stripe boundary. This LR asymmetry was initiated by a LR-biased migration of cells at stripe boundary, which later generated a velocity gradient propagating from stripe boundary to the center. After a series of cell translocations and rotations, ultimately, an LR-biased cell orientation within the micropatterned stripe was formed. Importantly, this initiation and propagation of LR asymmetry was observed only on rigid but not on soft substrates, suggesting that the LR asymmetry was regulated by rigid substrate probably through the organization of actin cytoskeleton. Together, we demonstrated substrate rigidity as a determinant factor that mediates the self-organizing LR asymmetry being unfolded from single cells to multicellular organization. More broadly, we anticipate that our findings would pave the way for rebuilding artificial tissue constructs with inherent LR asymmetry in the future.

Tyrosine phosphorylation/dephosphorylation of myosin II essential light chains of Entamoeba histolytica trophozoites regulates their motility

Entamoeba histolytica trophozoites dwell in the human intestine as comensals although under still unclear circumstances become invasive and destroy the host tissues. For these activities, trophozoites relay on remarkable motility provided by the cytoskeleton organization. Amebic actin and some of its actin-associated proteins are well known, while components of the myosin II molecule, although predicted from the E. histolytica genome, need biochemical and functional characterization. Recently, an amebic essential light myosin II chain, named EhMLCI, was identified and reported to be phosphorylated in tyrosines. The phosphorylated form of the protein was associated with the soluble assembly incompetent conformation of the heavy myosin chains, while the non-phosphorylated protein was identified with filamentous heavy chains, organized in an assembly competent conformation. It was postulated that EhMLCI tyrosine phosphorylation could act as a negative regulator of myosin II activity by its phosphorylation/dephosphorylation cycles. To test this hypothesis, we constructed an expression vector containing an EhMLCI DNA sequence where two tyrosine residues, with strong probability of phosphorylation and fall within the single EF-hand domain that interacts with the N-terminus of myosin II heavy chains, were replaced by phenylalanines. Transfected trophozoites, expressing the mutant MutEhMLCI protein cannot process it, thereby not incorporated into the phosphorylation/dephosphorylation cycles required for myosin II activity, results in motility defective trophozoites.

Discovery of novel peptides targeting pro-atherogenic endothelium in disturbed flow regions -Targeted siRNA delivery to pro-atherogenic endothelium in vivo

Atherosclerosis occurs preferentially in arterial regions exposed to disturbed blood flow. Targeting these pro-atherogenic regions is a potential anti-atherogenic therapeutic approach, but it has been extremely challenging. Here, using in vivo phage display approach and the partial carotid ligation model of flow-induced atherosclerosis in mouse, we identified novel peptides that specifically bind to endothelial cells (ECs) exposed to disturbed flow condition in pro-atherogenic regions. Two peptides, CLIRRTSIC and CPRRSHPIC, selectively bound to arterial ECs exposed to disturbed flow not only in the partially ligated carotids but also in the lesser curvature and branching point of the aortic arch in mice as well as human pulmonary artery branches. Peptides were conjugated to branched polyethylenimine-polyethylene glycol polymer to generate polyplexes carrying siRNA targeting intercellular adhesion molecule-1 (siICAM-1). In mouse model, CLIRRTSIC polyplexes carrying si-ICAM-1 specifically bound to endothelium in disturbed flow regions, reducing endothelial ICAM-1 expression. Mass spectrometry analysis revealed that non-muscle myosin heavy chain II A (NMHC IIA) is a protein targeted by CLIRRTSIC peptide. Further studies showed that shear stress regulates NMHC IIA expression and localization in ECs. The CLIRRTSIC is a novel peptide that could be used for targeted delivery of therapeutics such as siRNAs to pro-atherogenic endothelium.

Matrix-driven Myosin II Mediates the Pro-fibrotic Fibroblast Phenotype

Pro-fibrotic mesenchymal cells are known to be the key effector cells of fibroproliferative disease, but the specific matrix signals and the induced cellular responses that drive the fibrogenic phenotype remain to be elucidated. The key mediators of the fibroblast fibrogenic phenotype were characterized using a novel assay system that measures fibroblast behavior in response to actual normal and fibrotic lung tissue. Using this system, we demonstrate that normal lung promotes fibroblast motility and polarization, while fibrotic lung immobilizes the fibroblast and promotes myofibroblast differentiation. These context-specific phenotypes are surprisingly both mediated by myosin II. The role of myosin II is supported by the observation of an increase in myosin phosphorylation and a change in intracellular distribution in fibroblasts on fibrotic lung, as compared with normal lung. Moreover, loss of myosin II activity has opposing effects on protrusive activity in fibroblasts on normal and fibrotic lung. Loss of myosin II also selectively inhibits myofibroblast differentiation in fibroblasts on fibrotic lung. Importantly, these findings are recapitulated by varying the matrix stiffness of polyacrylamide gels in the range of normal and fibrotic lung tissue. Comparison of the effects of myosin inhibition on lung tissue with that of polyacrylamide gels suggests that matrix fiber organization drives the fibroblast phenotype under conditions of normal/soft lung, while matrix stiffness drives the phenotype under conditions of fibrotic/stiff lung. This work defines novel roles for myosin II as a key regulatory effector molecule of the pro-fibrotic phenotype, in response to biophysical properties of the matrix.