Articles de revues : « Non muscle myosin II A »

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Watanabe, T., H. Hosoya et S. Yonemura. « 1P205 Live imaging of Non-muscle myosin II in epithelial cells ». Seibutsu Butsuri 45, supplement (2005) : S83. http://dx.doi.org/10.2142/biophys.45.s83_1.

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Ubukawa, Kumi, Yong-Mei Guo, Masayuki Takahashi, Makoto Hirokawa, Yoshihiro Michishita, Miho Nara, Hiroyuki Tagawa et al. « Enucleation of human erythroblasts involves non-muscle myosin IIB ». Blood 119, n^o 4 (26 janvier 2012) : 1036–44. http://dx.doi.org/10.1182/blood-2011-06-361907.

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Abstract Mammalian erythroblasts undergo enucleation, a process thought to be similar to cytokinesis. Although an assemblage of actin, non-muscle myosin II, and several other proteins is crucial for proper cytokinesis, the role of non-muscle myosin II in enucleation remains unclear. In this study, we investigated the effect of various cell-division inhibitors on cytokinesis and enucleation. For this purpose, we used human colony-forming unit-erythroid (CFU-E) and mature erythroblasts generated from purified CD34+ cells as target cells for cytokinesis and enucleation assay, respectively. Here we show that the inhibition of myosin by blebbistatin, an inhibitor of non-muscle myosin II ATPase, blocks both cell division and enucleation, which suggests that non-muscle myosin II plays an essential role not only in cytokinesis but also in enucleation. When the function of non-muscle myosin heavy chain (NMHC) IIA or IIB was inhibited by an exogenous expression of myosin rod fragment, myosin IIA or IIB, each rod fragment blocked the proliferation of CFU-E but only the rod fragment for IIB inhibited the enucleation of mature erythroblasts. These data indicate that NMHC IIB among the isoforms is involved in the enucleation of human erythroblasts.

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Dasbiswas, Kinjal, Shiqiong Hu, Frank Schnorrer, Samuel A. Safran et Alexander D. Bershadsky. « Ordering of myosin II filaments driven by mechanical forces : experiments and theory ». Philosophical Transactions of the Royal Society B : Biological Sciences 373, n^o 1747 (9 avril 2018) : 20170114. http://dx.doi.org/10.1098/rstb.2017.0114.

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Myosin II filaments form ordered superstructures in both cross-striated muscle and non-muscle cells. In cross-striated muscle, myosin II (thick) filaments, actin (thin) filaments and elastic titin filaments comprise the stereotypical contractile units of muscles called sarcomeres. Linear chains of sarcomeres, called myofibrils, are aligned laterally in registry to form cross-striated muscle cells. The experimentally observed dependence of the registered organization of myofibrils on extracellular matrix elasticity has been proposed to arise from the interactions of sarcomeric contractile elements (considered as force dipoles) through the matrix. Non-muscle cells form small bipolar filaments built of less than 30 myosin II molecules. These filaments are associated in registry forming superstructures (‘stacks’) orthogonal to actin filament bundles. Formation of myosin II filament stacks requires the myosin II ATPase activity and function of the actin filament crosslinking, polymerizing and depolymerizing proteins. We propose that the myosin II filaments embedded into elastic, intervening actin network (IVN) function as force dipoles that interact attractively through the IVN. This is in analogy with the theoretical picture developed for myofibrils where the elastic medium is now the actin cytoskeleton itself. Myosin stack formation in non-muscle cells provides a novel mechanism for the self-organization of the actin cytoskeleton at the level of the entire cell. This article is part of the theme issue ‘Self-organization in cell biology’.

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Wrighton, Katharine H. « Non-muscle myosin II in kidney morphogenesis ». Nature Reviews Nephrology 13, n^o 7 (30 mai 2017) : 384. http://dx.doi.org/10.1038/nrneph.2017.77.

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Levinson, Howard, Blaine Mischen, Bruce Klitzman, Detlev Erdmann et L. Scott Levin. « Non muscle myosin II regulates contractile phenotypes ». Journal of the American College of Surgeons 205, n^o 3 (septembre 2007) : S60—S61. http://dx.doi.org/10.1016/j.jamcollsurg.2007.06.148.

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Maciver, Sutherland K. « Myosin II function in non-muscle cells ». BioEssays 18, n^o 3 (mars 1996) : 179–82. http://dx.doi.org/10.1002/bies.950180304.

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Porro, Chiara, Antonio Pennella, Maria Antonietta Panaro et Teresa Trotta. « Functional Role of Non-Muscle Myosin II in Microglia : An Updated Review ». International Journal of Molecular Sciences 22, n^o 13 (22 juin 2021) : 6687. http://dx.doi.org/10.3390/ijms22136687.

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Myosins are a remarkable superfamily of actin-based motor proteins that use the energy derived from ATP hydrolysis to translocate actin filaments and to produce force. Myosins are abundant in different types of tissues and involved in a large variety of cellular functions. Several classes of the myosin superfamily are expressed in the nervous system; among them, non-muscle myosin II (NM II) is expressed in both neurons and non-neuronal brain cells, such as astrocytes, oligodendrocytes, endothelial cells, and microglia. In the nervous system, NM II modulates a variety of functions, such as vesicle transport, phagocytosis, cell migration, cell adhesion and morphology, secretion, transcription, and cytokinesis, as well as playing key roles during brain development, inflammation, repair, and myelination functions. In this review, we will provide a brief overview of recent emerging roles of NM II in resting and activated microglia cells, the principal regulators of immune processes in the central nervous system (CNS) in both physiological and pathological conditions. When stimulated, microglial cells react and produce a number of mediators, such as pro-inflammatory cytokines, free radicals, and nitric oxide, that enhance inflammation and contribute to neurodegenerative diseases. Inhibition of NM II could be a new therapeutic target to treat or to prevent CNS diseases.

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Takubo, T., S. Wakui, K. Daigo, K. Kurokata, T. Ohashi, K. Katayama et M. Hino. « Expression of non-muscle type myosin heavy polypeptide 9 (MYH9) in mammalian cells ». European Journal of Histochemistry 47, n^o 4 (26 juin 2009) : 345. http://dx.doi.org/10.4081/845.

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Myosin is a functional protein associated with cellular movement, cell division, muscle contraction and other functions. Members of the myosin super-family are distinguished from the myosin heavy chains that play crucial roles in cellular processes. Although there are many studies of myosin heavy chains in this family, there are fewer on non-muscle myosin heavy chains than of muscle myosin heavy chains. Myosin is classified as type I (myosin I) or type II (myosin II). Myosin I, called unconventional myosin or mini-myosin, has one head, while myosin II, called conventional myosin, has two heads. We transfected myosin heavy polypeptide 9 (MYH9) into HeLa cells as a fusion protein with enhanced green fluorescent protein (EGFP) and analyzed the localization and distribution of MYH9 in parallel with those of actin and tubulin. The results indicate that MYH9 colocalizes with actin stress fibers. Since it has recently been shown by genetic analysis that autosomal dominant giant platelet syndromes are MYH9-related disorders, our development of transfected EGFP-MYH9 might be useful for predicting the associations between the function of actin polymerization, the MYH9 motor domain, and these disorders.

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Juanes-García, Alba, Clara Llorente-González et Miguel Vicente-Manzanares. « Molecular control of non-muscle myosin II assembly ». Oncotarget 7, n^o 5 (18 janvier 2016) : 5092–93. http://dx.doi.org/10.18632/oncotarget.6936.

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Wan, Xiaohu. « Counting Molecules in Non-Muscle Myosin II Filaments ». Biophysical Journal 108, n^o 2 (janvier 2015) : 322a. http://dx.doi.org/10.1016/j.bpj.2014.11.1750.

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Grinnell, F., et C. H. Ho. « Non-muscle myosin II heavy chain has a cryptic cell-adhesion domain ». Biochemical Journal 309, n^o 2 (15 juillet 1995) : 569–74. http://dx.doi.org/10.1042/bj3090569.

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We have discovered a cryptic cell-adhesion domain in non-muscle myosin II heavy chain. A 205 kDa cell-adhesion-promoting polypeptide (p205) was extracted from BHK cells by Nonidet P-40 or Dounce homogenization. Adhesion to p205 was specifically inhibited by the peptide Gly-Arg-Gly-Asp-Ser-Pro, indicating a role for the Arg-Gly-Asp cell-adhesion motif. Purified p205 was identified as non-muscle myosin II heavy chain, based on sequence analysis and on the cross-reactivity of p205 with anti-(bovine trachea myosin) antibodies. Further experiments showed that the heavy chain of purified myosin II has cell-adhesion-promoting activity in a cell-blotting assay, and cross-reacted with anti-p205 antibodies. Finally, the adhesion domain was located in the tail portion of myosin II heavy chain, where an Arg-Gly-Asp-containing sequence can be found.

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Kolega, J. « Cytoplasmic dynamics of myosin IIA and IIB : spatial ‘sorting’ of isoforms in locomoting cells ». Journal of Cell Science 111, n^o 15 (1 août 1998) : 2085–95. http://dx.doi.org/10.1242/jcs.111.15.2085.

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Different isoforms of non-muscle myosin II have different distributions in vivo, even within individual cells. In order to understand how these different distributions arise, the distribution and dynamics of non-muscle myosins IIA and myosin IIB were examined in cultured cells using immunofluorescence staining and time-lapse imaging of fluorescent analogs. Cultured bovine aortic endothelia contained both myosins IIA and IIB. Both isoforms distributed along stress fibers, in linear or punctate aggregates within lamellipodia, and diffusely around the nucleus. However, the A isoform was preferentially located toward the leading edge of migrating cells when compared with myosin IIB by double immunofluorescence staining. Conversely, the B isoform was enriched in structures at the cells' trailing edges. When fluorescent analogs of the two isoforms were co-injected into living cells, the injected myosins distributed with the same disparate localizations as endogenous myosins IIA and IIB. This indicated that the ability of the myosins to ‘sort’ within the cytoplasm is intrinsic to the proteins themselves, and not a result of localized synthesis or degradation. Furthermore, time-lapse imaging of injected analogs in living cells revealed differences in the rates at which the two isoforms rearranged during cell movement. The A isoform appeared in newly formed structures more rapidly than the B isoform, and was also lost more rapidly when structures disassembled. These observations suggest that the different localizations of myosins IIA and IIB reflect different rates at which the isoforms transit through assembly, movement and disassembly within the cell. The relative proportions of different myosin II isoforms within a particular cell type may determine the lifetimes of various myosin II-based structures in that cell.

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Johnson, Chloe A., Jake E. McGreig, Sarah T. Jeanfavre, Jonathan Walklate, Carlos D. Vera, Marta Farré, Daniel P. Mulvihill et al. « Identification of sequence changes in myosin II that adjust muscle contraction velocity ». PLOS Biology 19, n^o 6 (10 juin 2021) : e3001248. http://dx.doi.org/10.1371/journal.pbio.3001248.

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The speed of muscle contraction is related to body size; muscles in larger species contract at slower rates. Since contraction speed is a property of the myosin isoform expressed in a muscle, we investigated how sequence changes in a range of muscle myosin II isoforms enable this slower rate of muscle contraction. We considered 798 sequences from 13 mammalian myosin II isoforms to identify any adaptation to increasing body mass. We identified a correlation between body mass and sequence divergence for the motor domain of the 4 major adult myosin II isoforms (β/Type I, IIa, IIb, and IIx), suggesting that these isoforms have adapted to increasing body mass. In contrast, the non-muscle and developmental isoforms show no correlation of sequence divergence with body mass. Analysis of the motor domain sequence of β-myosin (predominant myosin in Type I/slow and cardiac muscle) from 67 mammals from 2 distinct clades identifies 16 sites, out of 800, associated with body mass (padj < 0.05) but not with the clade (padj > 0.05). Both clades change the same small set of amino acids, in the same order from small to large mammals, suggesting a limited number of ways in which contraction velocity can be successfully manipulated. To test this relationship, the 9 sites that differ between human and rat were mutated in the human β-myosin to match the rat sequence. Biochemical analysis revealed that the rat–human β-myosin chimera functioned like the native rat myosin with a 2-fold increase in both motility and in the rate of ADP release from the actin–myosin crossbridge (the step that limits contraction velocity). Thus, these sequence changes indicate adaptation of β-myosin as species mass increased to enable a reduced contraction velocity and heart rate.

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Daneshparvar, Nadia, Dianne W. Taylor, Thomas S. O’Leary, Hamidreza Rahmani, Fatemeh Abbasiyeganeh, Michael J. Previs et Kenneth A. Taylor. « CryoEM structure of Drosophila flight muscle thick filaments at 7 Å resolution ». Life Science Alliance 3, n^o 8 (27 juillet 2020) : e202000823. http://dx.doi.org/10.26508/lsa.202000823.

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Striated muscle thick filaments are composed of myosin II and several non-myosin proteins. Myosin II’s long α-helical coiled-coil tail forms the dense protein backbone of filaments, whereas its N-terminal globular head containing the catalytic and actin-binding activities extends outward from the backbone. Here, we report the structure of thick filaments of the flight muscle of the fruit fly Drosophila melanogaster at 7 Å resolution. Its myosin tails are arranged in curved molecular crystalline layers identical to flight muscles of the giant water bug Lethocerus indicus. Four non-myosin densities are observed, three of which correspond to ones found in Lethocerus; one new density, possibly stretchin-mlck, is found on the backbone outer surface. Surprisingly, the myosin heads are disordered rather than ordered along the filament backbone. Our results show striking myosin tail similarity within flight muscle filaments of two insect orders separated by several hundred million years of evolution.

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Park, Inju, Cecil Han, Sora Jin, Boyeon Lee, Heejin Choi, Jun Tae Kwon, Dongwook Kim et al. « Myosin regulatory light chains are required to maintain the stability of myosin II and cellular integrity ». Biochemical Journal 434, n^o 1 (27 janvier 2011) : 171–80. http://dx.doi.org/10.1042/bj20101473.

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Myosin II is an actin-binding protein composed of MHC (myosin heavy chain) IIs, RLCs (regulatory light chains) and ELCs (essential light chains). Myosin II expressed in non-muscle tissues plays a central role in cell adhesion, migration and division. The regulation of myosin II activity is known to involve the phosphorylation of RLCs, which increases the Mg2+-ATPase activity of MHC IIs. However, less is known about the details of RLC–MHC II interaction or the loss-of-function phenotypes of non-muscle RLCs in mammalian cells. In the present paper, we investigate three highly conserved non-muscle RLCs of the mouse: MYL (myosin light chain) 12A (referred to as MYL12A), MYL12B and MYL9 (MYL12A/12B/9). Proteomic analysis showed that all three are associated with the MHCs MYH9 (NMHC IIA) and MYH10 (NMHC IIB), as well as the ELC MYL6, in NIH 3T3 fibroblasts. We found that knockdown of MYL12A/12B in NIH 3T3 cells results in striking changes in cell morphology and dynamics. Remarkably, the levels of MYH9, MYH10 and MYL6 were reduced significantly in knockdown fibroblasts. Comprehensive interaction analysis disclosed that MYL12A, MYL12B and MYL9 can all interact with a variety of MHC IIs in diverse cell and tissue types, but do so optimally with non-muscle types of MHC II. Taken together, our study provides direct evidence that normal levels of non-muscle RLCs are essential for maintaining the integrity of myosin II, and indicates that the RLCs are critical for cell structure and dynamics.

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Eliott, S., P. H. Vardy et K. L. Williams. « The distribution of myosin II in Dictyostelium discoideum slug cells. » Journal of Cell Biology 115, n^o 5 (1 décembre 1991) : 1267–74. http://dx.doi.org/10.1083/jcb.115.5.1267.

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While the role of myosin II in muscle contraction has been well characterized, less is known about the role of myosin II in non-muscle cells. Recent molecular genetic experiments on Dictyostelium discoideum show that myosin II is necessary for cytokinesis and multicellular development. Here we use immunofluorescence microscopy with monoclonal and polyclonal antimyosin antibodies to visualize myosin II in cells of the multicellular D. discoideum slug. A subpopulation of peripheral and anterior cells label brightly with antimyosin II antibodies, and many of these cells display a polarized intracellular distribution of myosin II. Other cells in the slug label less brightly and their cytoplasm displays a more homogeneous distribution of myosin II. These results provide insight into cell motility within a three-dimensional tissue and they are discussed in relation to the possible roles of myosin II in multicellular development.

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Kim, Jong-Hee, et LaDora V. Thompson. « Non-weight bearing-induced muscle weakness : the role of myosin quantity and quality in MHC type II fibers ». American Journal of Physiology-Cell Physiology 307, n^o 2 (15 juillet 2014) : C190—C194. http://dx.doi.org/10.1152/ajpcell.00076.2014.

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We tested the hypothesis that non-weight bearing-induced muscle weakness (i.e., specific force) results from decreases in myosin protein quantity (i.e., myosin content per half-sarcomere and the ratio of myosin to actin) and quality (i.e., force per half-sarcomere and population of myosin heads in the strong-binding state during muscle contraction) in single myosin heavy chain (MHC) type II fibers. Fisher-344 rats were assigned to weight-bearing control (Con) or non-weight bearing (NWB). The NWB rats were hindlimb unloaded for 2 wk. Diameter, force, and MHC content were determined in permeabilized single fibers from the semimembranosus muscle. MHC isoform and the ratio of MHC to actin in each fiber were determined by gel electrophoresis and silver staining techniques. The structural distribution of myosin from spin-labeled fiber bundles during maximal isometric contraction was evaluated using electron paramagnetic resonance spectroscopy. Specific force (peak force per cross-sectional area) in MHC type IIB and IIXB fibers from NWB was significantly reduced by 38% and 18%, respectively. MHC content per half-sarcomere was significantly reduced by 21%. Two weeks of hindlimb unloading resulted in a reduced force per half-sarcomere of 52% and fraction of myosin strong-binding during contraction of 34%. The results suggest that reduced myosin and actin content (quantity) and myosin quality concomitantly contribute to non-weight bearing-related muscle weakness.

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Agarwal, Priti, et Ronen Zaidel-Bar. « Diverse roles of non-muscle myosin II contractility in 3D cell migration ». Essays in Biochemistry 63, n^o 5 (24 septembre 2019) : 497–508. http://dx.doi.org/10.1042/ebc20190026.

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Abstract All is flux, nothing stays still. Heraclitus of Ephesus’ characterization of the universe holds true for cells within animals and for proteins within cells. In this review, we examine the dynamics of actin and non-muscle myosin II within cells, and how their dynamics power the movement of cells within tissues. The 3D environment that migrating cells encounter along their path also changes over time, and cells can adopt various mechanisms of motility, depending on the topography, mechanics and chemical composition of their surroundings. We describe the differential spatio-temporal regulation of actin and myosin II-mediated contractility in mesenchymal, lobopodial, amoeboid, and swimming modes of cell migration. After briefly reviewing the biochemistry of myosin II, we discuss the role actomyosin contractility plays in the switch between modes of 3D migration that cells use to adapt to changing environments.

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Verkhovsky, A. B., et G. G. Borisy. « Non-sarcomeric mode of myosin II organization in the fibroblast lamellum. » Journal of Cell Biology 123, n^o 3 (1 novembre 1993) : 637–52. http://dx.doi.org/10.1083/jcb.123.3.637.

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The organization of myosin in the fibroblast lamellum was studied by correlative fluorescence and electron microscopy after a novel procedure to reveal its underlying morphology. An X-rhodamine analog of conventional smooth muscle myosin (myosin II) that colocalized after microinjection with endogenous myosin was used to trace myosin distribution in living fibroblasts. Then, the same cells were examined by EM of platinum replicas. To visualize the structural arrangement of myosin, other cytoskeletal fibrillar structures had to be removed: microtubules were depolymerized by nocodazole treatment of the living cells before injection of myosin; continued nocodazole treatment also induced the intermediate filaments to concentrate near the nucleus, thus removing them from the lamellar region; actin filaments were removed after lysis of the cells by incubation of the cytoskeletons with recombinant gelsolin. Possible changes in myosin organization caused by this treatment were examined by fluorescence microscopy. No significant differences in myosin distribution patterns between nocodazole-treated and control cells were observed. Cell lysis and depletion of actin also did not induce reorganization of myosin as was shown by direct comparison of myosin distribution in the same cells in the living state and after gelsolin treatment. EM of the well-spread, peripheral regions of actin-depleted cytoskeletons revealed a network of bipolar myosin mini-filaments, contracting each other at their terminal, globular regions. The morphology of this network corresponded well to the myosin distribution observed by fluorescence microscopy. A novel mechanism of cell contraction by folding of the myosin filament network is proposed.

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Matsui, Tsubasa S., Roland Kaunas, Makoto Kanzaki, Masaaki Sato et Shinji Deguchi. « Non-muscle myosin II induces disassembly of actin stress fibres independently of myosin light chain dephosphorylation ». Interface Focus 1, n^o 5 (3 août 2011) : 754–66. http://dx.doi.org/10.1098/rsfs.2011.0031.

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Dynamic remodelling of actin stress fibres (SFs) allows non-muscle cells to adapt to applied forces such as uniaxial cell shortening. However, the mechanism underlying rapid and selective disassembly of SFs oriented in the direction of shortening remains to be elucidated. Here, we investigated how myosin crossbridge cycling induced by MgATP is associated with SF disassembly. Moderate concentrations of MgATP, or [MgATP], induced SF contraction. Meanwhile, at [MgATP] slightly higher than the physiological level, periodic actin patterns emerged along the length of SFs and dispersed within seconds. The actin fragments were diverse in length, but comparable to those in characteristic sarcomeric units of SFs. These results suggest that MgATP-bound non-muscle myosin II dissociates from the individual actin filaments that constitute the sarcomeric units, resulting in unbundling-induced disassembly rather than end-to-end actin depolymerization. This rapid SF disassembly occurred independent of dephosphorylation of myosin light chain. In terms of effects on actin–myosin interactions, a rise in [MgATP] is functionally equivalent to a temporal decrease in the total number of actin–myosin crossbridges. Actin–myosin crossbridges are known to be reduced by an assisting load on myosin. Thus, the present study suggests that reducing the number of actin–myosin crossbridges promotes rapid and orientation-dependent disassembly of SFs after cell shortening.

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Newell-Litwa, K. A., R. Horwitz et M. L. Lamers. « Non-muscle myosin II in disease : mechanisms and therapeutic opportunities ». Disease Models & ; Mechanisms 8, n^o 12 (5 novembre 2015) : 1495–515. http://dx.doi.org/10.1242/dmm.022103.

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West-Foyle, Hoku, Priyanka Kothari, Jonathan Osborne et Douglas N. Robinson. « 14-3-3 proteins tune non-muscle myosin II assembly ». Journal of Biological Chemistry 293, n^o 18 (16 mars 2018) : 6751–61. http://dx.doi.org/10.1074/jbc.m117.819391.

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Schewkunow, Vitali, Karan P. Sharma, Gerold Diez, Anna H. Klemm, Pal C. Sharma et Wolfgang H. Goldmann. « Thermodynamic evidence of non-muscle myosin II–lipid-membrane interaction ». Biochemical and Biophysical Research Communications 366, n^o 2 (février 2008) : 500–505. http://dx.doi.org/10.1016/j.bbrc.2007.11.170.

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Verkhovsky, A. B., T. M. Svitkina et G. G. Borisy. « Polarity sorting of actin filaments in cytochalasin-treated fibroblasts ». Journal of Cell Science 110, n^o 15 (1 août 1997) : 1693–704. http://dx.doi.org/10.1242/jcs.110.15.1693.

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The polarity of actin filaments is fundamental for the subcellular mechanics of actin-myosin interaction; however, little is known about how actin filaments are oriented with respect to myosin in non-muscle cells and how actin polarity organization is established and maintained. Here we approach these questions by investigating changes in the organization and polarity of actin relative to myosin II during actin filament translocation. Actin and myosin II reorganization was followed both kinetically, using microinjected fluorescent analogs of actin and myosin, and ultrastructurally, using myosin S1 decoration and immunogold labelling, in cultured fibroblasts that were induced to contract by treatment with cytochalasin D. We observed rapid (within 15 minutes) formation of ordered actin filament arrays: short tapered bundles and aster-like assemblies, in which filaments had uniform polarity with their barbed ends oriented toward the aggregate of myosin II at the base of a bundle or in the center of an aster. The resulting asters further interacted with each other and aggregated into bigger asters. The arrangement of actin in asters was in sharp contrast to the mixed polarity of actin filaments relative to myosin in non-treated cells. At the edge of the cell, actin filaments became oriented with their barbed ends toward the cell center; that is, the orientation was opposite to what was observed at the edge of nontreated cells. This rearrangement is indicative of relative translocation of actin and myosin II and of the ability of myosin II to sort actin filaments with respect to their polarity during translocation. The results suggest that the myosin II-actin system of non-muscle cells is organized as a dynamic network where actin filament arrangement is defined in the course of its interaction with myosin II.

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Wang, Kui, Zhifang Yang, Xiaohui Chen, Shunxiao Liu, Xiang Li, Liuhao Wang, Hao Yu et Hongwei Zhang. « Characterization and analysis of myosin gene family in the whitefly (<i>Bemisia tabaci</i>) ». AIMS Molecular Science 9, n^o 2 (2022) : 91–106. http://dx.doi.org/10.3934/molsci.2022006.

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<abstract> <p>Myosin is an actin-based motor protein that widely exists in muscle tissue and non-muscle tissue, and myosin of a diverse subfamily has obvious differences in structure and cell function. Many eukaryotes and even some unicellular organisms possess a variety of myosins. They have been well characterized in human, fungi and other organisms. However, the myosin gene family in <italic>Bemisia tabaci</italic> MEAM1 (Middle East-Asia Minor1 species) is poorly studied. In the study, we identified 15 myosin genes in <italic>B. tabaci</italic> MEAM1 based on a genome database. Myosin genes can be divided into ten classes, including subfamilies I, II, III, V, VI, VII, IX, XV, XVIII, XX in <italic>B. tabaci</italic> MEAM1. The amounts of myosin in Class I are the largest of the isoforms. Expression profiling of myosins by quantitative real-time PCR revealed that their expression differed among developmental stages and different tissues of <italic>B. tabaci</italic> MEAM1. The diversely may be related to the development characteristics of <italic>B. tabaci</italic> MEAM1. The <italic>BtaMyo-IIIb-like X1</italic> was highly expressed in nymphs 4 instar which may be related to the development process before metamorphosis. Our outcome contributes to the basis for further research on myosin gene function in <italic>B. tabaci</italic> MEAM1 and homologous myosins in other biology.</p> </abstract>

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Javier-Torrent, Míriam, et Carlos A. Saura. « Conventional and Non-Conventional Roles of Non-Muscle Myosin II-Actin in Neuronal Development and Degeneration ». Cells 9, n^o 9 (19 août 2020) : 1926. http://dx.doi.org/10.3390/cells9091926.

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Myosins are motor proteins that use chemical energy to produce mechanical forces driving actin cytoskeletal dynamics. In the brain, the conventional non-muscle myosin II (NMII) regulates actin filament cytoskeletal assembly and contractile forces during structural remodeling of axons and dendrites, contributing to morphology, polarization, and migration of neurons during brain development. NMII isoforms also participate in neurotransmission and synaptic plasticity by driving actin cytoskeletal dynamics during synaptic vesicle release and retrieval, and formation, maturation, and remodeling of dendritic spines. NMIIs are expressed differentially in cerebral non-neuronal cells, such as microglia, astrocytes, and endothelial cells, wherein they play key functions in inflammation, myelination, and repair. Besides major efforts to understand the physiological functions and regulatory mechanisms of NMIIs in the nervous system, their contributions to brain pathologies are still largely unclear. Nonetheless, genetic mutations or deregulation of NMII and its regulatory effectors are linked to autism, schizophrenia, intellectual disability, and neurodegeneration, indicating non-conventional roles of NMIIs in cellular mechanisms underlying neurodevelopmental and neurodegenerative disorders. Here, we summarize the emerging biological roles of NMIIs in the brain, and discuss how actomyosin signaling contributes to dysfunction of neurons and glial cells in the context of neurological disorders. This knowledge is relevant for a deep understanding of NMIIs on the pathogenesis and therapeutics of neuropsychiatric and neurodegenerative diseases.

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Moura, Pedro L., Bethan R. Hawley, Tosti J. Mankelow, Rebecca E. Griffiths, Johannes G. G. Dobbe, Geert J. Streekstra, David J. Anstee, Timothy J. Satchwell et Ashley M. Toye. « Non-muscle myosin II drives vesicle loss during human reticulocyte maturation ». Haematologica 103, n^o 12 (3 août 2018) : 1997–2007. http://dx.doi.org/10.3324/haematol.2018.199083.

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Betapudi, Venkaiah, Linda Hsi, Kristi L. Allen, Belinda Willard et Keith R. McCrae. « Non-Muscle Myosin II Mediates Microparticle Release From Endothelial Cells Activated by Antiphospholipid Antibodies »,. Blood 118, n^o 21 (18 novembre 2011) : 3343. http://dx.doi.org/10.1182/blood.v118.21.3343.3343.

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Abstract Abstract 3343 The antiphospholipid syndrome (APS) is characterized by thrombosis and recurrent fetal loss in patients with antiphospholipid antibodies (APLA). The majority of pathogenic APLA are actually directed against β2-glycoprotein I (β2GPI), an abundant plasma phospholipid binding protein. Microparticles are small phospholipid-rich vesicles that may express tissue factor and are thought to play an important role in thrombosis. Increased release of microparticles may be stimulated by cellular activation or apoptosis, and previous work from our laboratory and others has demonstrated increased levels of circulating microparticles in patients with APS, even far removed from thrombotic events. Though several mechanisms have been proposed for mediating release of microparticles from cells, this process is poorly understood and there is little information available concerning the mechanisms of microparticle release from endothelial cells stimulated by APLA/anti-β2GPI antibodies. To address this issue we assessed the role of non-muscle myosin II motor protein in mediating the release of microparticles from endothelial cells activated by anti-β2GPI antibodies. We observed that incubation of endothelial cells with β2GPI and anti-β2GPI antibodies caused significant increases in the release of microparticles compared to cells treated with β2GPI and control antibodies. Proteomic and biochemical studies demonstrated that anti-β2GPI antibodies caused increased phosphorylation of endothelial cell Myosin II light chain (MLC), an essential step in the activation of Myosin II motor protein. Moreover, examination of endothelial cells stimulated by anti-β2GPI antibodies using confocal microscopy revealed a dramatic increase in the formation of actin-myosin II filaments. To assess the effects of these changes on microparticle release, we inhibited MLC phosphorylation in anti-β2GPI-treated endothelial cells using ML-7, a highly specific inhibitor of MLC. ML-7 caused a significant decrease in the release of microparticles from anti-β2GPI-treated cells. In conclusion, our results demonstrate that non-muscle myosin II motor protein activation by anti-β2GPI antibodies is necessary for the increased release of microparticles from activated cells. These microparticles may play important roles in the propagation of thrombosis and other clinical sequelae observed in patients with APS. Disclosures: No relevant conflicts of interest to declare.

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Kondo, Tomo, Kozue Hamao, Keiju Kamijo, Hiroshi Kimura, Makiko Morita, Masayuki Takahashi et Hiroshi Hosoya. « Enhancement of myosin II/actin turnover at the contractile ring induces slower furrowing in dividing HeLa cells ». Biochemical Journal 435, n^o 3 (13 avril 2011) : 569–76. http://dx.doi.org/10.1042/bj20100837.

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Myosin II ATPase activity is enhanced by the phosphorylation of MRLC (myosin II regulatory light chain) in non-muscle cells. It is well known that pMRLC (phosphorylated MRLC) co-localizes with F-actin (filamentous actin) in the CR (contractile ring) of dividing cells. Recently, we reported that HeLa cells expressing non-phosphorylatable MRLC show a delay in the speed of furrow ingression, suggesting that pMRLC plays an important role in the control of furrow ingression. However, it is still unclear how pMRLC regulates myosin II and F-actin at the CR to control furrow ingression during cytokinesis. In the present study, to clarify the roles of pMRLC, we measured the turnover of myosin II and actin at the CR in dividing HeLa cells expressing fluorescent-tagged MRLCs and actin by FRAP (fluorescence recovery after photobleaching). A myosin II inhibitor, blebbistatin, caused an enhancement of the turnover of MRLC and actin at the CR, which induced a delay in furrow ingression. Furthermore, only non-phosphorylatable MRLC and a Rho-kinase inhibitor, Y-27632, accelerated the turnover of MRLC and actin at the CR. Interestingly, the effect of Y-27632 was cancelled in the cell expressing phosphomimic MRLCs. Taken together, these results reveal that pMRLC reduces the turnover of myosin II and also actin at the CR. In conclusion, we show that the enhancement of myosin II and actin turnover at the CR induced slower furrowing in dividing HeLa cells.

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Marcucci, Lorenzo, Hiroki Fukunaga, Toshio Yanagida et Mitsuhiro Iwaki. « The Synergic Role of Actomyosin Architecture and Biased Detachment in Muscle Energetics : Insights in Cross Bridge Mechanism beyond the Lever-Arm Swing ». International Journal of Molecular Sciences 22, n^o 13 (29 juin 2021) : 7037. http://dx.doi.org/10.3390/ijms22137037.

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Muscle energetics reflects the ability of myosin motors to convert chemical energy into mechanical energy. How this process takes place remains one of the most elusive questions in the field. Here, we combined experimental measurements of in vitro sliding velocity based on DNA-origami built filaments carrying myosins with different lever arm length and Monte Carlo simulations based on a model which accounts for three basic components: (i) the geometrical hindrance, (ii) the mechano-sensing mechanism, and (iii) the biased kinetics for stretched or compressed motors. The model simulations showed that the geometrical hindrance due to acto-myosin spatial mismatching and the preferential detachment of compressed motors are synergic in generating the rapid increase in the ATP-ase rate from isometric to moderate velocities of contraction, thus acting as an energy-conservation strategy in muscle contraction. The velocity measurements on a DNA-origami filament that preserves the motors’ distribution showed that geometrical hindrance and biased detachment generate a non-zero sliding velocity even without rotation of the myosin lever-arm, which is widely recognized as the basic event in muscle contraction. Because biased detachment is a mechanism for the rectification of thermal fluctuations, in the Brownian-ratchet framework, we predict that it requires a non-negligible amount of energy to preserve the second law of thermodynamics. Taken together, our theoretical and experimental results elucidate less considered components in the chemo-mechanical energy transduction in muscle.

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Bond, Lisa M., Hemma Brandstaetter, James R. Sellers, John Kendrick-Jones et Folma Buss. « Myosin motor proteins are involved in the final stages of the secretory pathways ». Biochemical Society Transactions 39, n^o 5 (21 septembre 2011) : 1115–19. http://dx.doi.org/10.1042/bst0391115.

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In eukaryotes, the final steps in both the regulated and constitutive secretory pathways can be divided into four distinct stages: (i) the ‘approach’ of secretory vesicles/granules to the PM (plasma membrane), (ii) the ‘docking’ of these vesicles/granules at the membrane itself, (iii) the ‘priming’ of the secretory vesicles/granules for the fusion process, and, finally, (iv) the ‘fusion’ of vesicular/granular membranes with the PM to permit content release from the cell. Recent work indicates that non-muscle myosin II and the unconventional myosin motor proteins in classes 1c/1e, Va and VI are specifically involved in these final stages of secretion. In the present review, we examine the roles of these myosins in these stages of the secretory pathway and the implications of their roles for an enhanced understanding of secretion in general.

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Vicente-Manzanares, Miguel, Xuefei Ma, Robert S. Adelstein et Alan Rick Horwitz. « Non-muscle myosin II takes centre stage in cell adhesion and migration ». Nature Reviews Molecular Cell Biology 10, n^o 11 (novembre 2009) : 778–90. http://dx.doi.org/10.1038/nrm2786.

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Snell, Nicole E. « Triple FRET Imaging of Non-Muscle Myosin II Localization in Migrating Cells ». Biophysical Journal 112, n^o 3 (février 2017) : 267a. http://dx.doi.org/10.1016/j.bpj.2016.11.1449.

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Chattoraj, Shyamtanu, Shekhar Saha, Debdatta Halder, Siddhartha S. Jana et Kankan Bhattacharyya. « Structural Oscillations of Non-muscle Myosin II-C2 : Time Resolved Confocal Microscopy ». ChemistrySelect 2, n^o 3 (23 janvier 2017) : 953–58. http://dx.doi.org/10.1002/slct.201601963.

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Wang, Aibing, Xuefei Ma, Mary Anne Conti et Robert S. Adelstein. « Distinct and redundant roles of the non-muscle myosin II isoforms and functional domains ». Biochemical Society Transactions 39, n^o 5 (21 septembre 2011) : 1131–35. http://dx.doi.org/10.1042/bst0391131.

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We propose that the in vivo functions of NM II (non-muscle myosin II) can be divided between those that depend on the N-terminal globular motor domain and those less dependent on motor activity but more dependent on the C-terminal domain. The former, being more dependent on the kinetic properties of NM II to translocate actin filaments, are less amenable to substitution by different NM II isoforms, whereas the in vivo functions of the latter, which involve the structural properties of NM II to cross-link actin filaments, are more amenable to substitution. In light of this hypothesis, we examine the ability of NM II-A, as well as a motor-compromised form of NM II-B, to replace NM II-B and rescue neuroepithelial cell–cell adhesion defects and hydrocephalus in the brain of NM II-B-depleted mice. We also examine the ability of NM II-B as well as chimaeric forms of NM II (II-A head and II-B tail and vice versa) to substitute for NM II-A in cell–cell adhesions in II-A-ablated mice. However, we also show that certain functions, such as neuronal cell migration in the developing brain and vascularization of the mouse embryo and placenta, specifically require NM II-B and II-A respectively.

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Chaudoir, B. M., P. A. Kowalczyk et R. L. Chisholm. « Regulatory light chain mutations affect myosin motor function and kinetics ». Journal of Cell Science 112, n^o 10 (15 mai 1999) : 1611–20. http://dx.doi.org/10.1242/jcs.112.10.1611.

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The actin-based motor protein myosin II plays a critical role in many cellular processes in both muscle and non-muscle cells. Targeted disruption of the Dictyostelium regulatory light chain (RLC) caused defects in cytokinesis and multicellular morphogenesis. In contrast, a myosin heavy chain mutant lacking the RLC binding site, and therefore bound RLC, showed normal cytokinesis and development. One interpretation of these apparently contradictory results is that the phenotypic defects in the RLC null mutant results from mislocalization of myosin caused by aggregation of RLC null myosin. To distinguish this from the alternative explanation that the RLC can directly influence myosin activity, we expressed three RLC point mutations (E12T, G18K and N94A) in a Dictyostelium RLC null mutant. The position of these mutations corresponds to the position of mutations that have been shown to result in familial hypertrophic cardiomyopathy in humans. Analysis of purified Dictyostelium myosin showed that while these mutations did not affect binding of the RLC to the MHC, its phosphorylation by myosin light chain kinase or regulation of its activity by phosphorylation, they resulted in decreased myosin function. All three mutants showed impaired cytokinesis in suspension, and one produced defective fruiting bodies with short stalks and decreased spore formation. The abnormal myosin localization seen in the RLC null mutant was restored to wild-type localization by expression of all three RLC mutants. Although two of the mutant myosins had wild-type actin-activated ATPase, they produced in vitro motility rates half that of wild type. N94A myosin showed a fivefold decrease in actin-ATPase and a similar decrease in the rate at which it moved actin in vitro. These results indicate that the RLC can play a direct role in determining the force transmission and kinetic properties of myosin.

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Hirota, Yuki, Alice Meunier, Shihhui Huang, Togo Shimozawa, Yasuyuki S. Kida, Masashi Inoue, Tsubasa Ito et al. « Planar cell polarity of multiciliated ependymal cells regulated by non-muscle myosin II ». Neuroscience Research 68 (janvier 2010) : e364. http://dx.doi.org/10.1016/j.neures.2010.07.1614.

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Nie, Wei, Ming-tzo Wei, H. Daniel Ou-Yang, Sabrina Jedlicka et Dimitrios Vavylonis. « Dynamics of Non-Muscle Myosin II Organization into Stress Fibers and Contractile Networks ». Biophysical Journal 104, n^o 2 (janvier 2013) : 140a. http://dx.doi.org/10.1016/j.bpj.2012.11.799.

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Liu, Zhenan, Elke Van Rossen, Jean-Pierre Timmermans, Albert Geerts, Leo A. van Grunsven et Hendrik Reynaert. « Distinct roles for non-muscle myosin II isoforms in mouse hepatic stellate cells ». Journal of Hepatology 54, n^o 1 (janvier 2011) : 132–41. http://dx.doi.org/10.1016/j.jhep.2010.06.020.

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Ho, Wei-Ting, Jung-Shen Chang, San-Fang Chou, Wei-Lun Hwang, Po-Jen Shih, Shu-Wen Chang, Muh-Hwa Yang, Tzuu-Shuh Jou et I.-Jong Wang. « Targeting non-muscle myosin II promotes corneal endothelial migration through regulating lamellipodial dynamics ». Journal of Molecular Medicine 97, n^o 9 (13 juillet 2019) : 1345–57. http://dx.doi.org/10.1007/s00109-019-01818-5.

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Kovari, Daniel T., Wenbin Wei, Jan-Simon Toro, Ruth E. Fogg, Karen Porter et Jennifer E. Curtis. « Frustrated Phagocytic Spreading Dynamics End in Distinct Non-Muscle Myosin II Dependent Contraction ». Biophysical Journal 110, n^o 3 (février 2016) : 621a. http://dx.doi.org/10.1016/j.bpj.2015.11.3330.

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Lee, Stacey, et Sanjay Kumar. « Actomyosin stress fiber mechanosensing in 2D and 3D ». F1000Research 5 (7 septembre 2016) : 2261. http://dx.doi.org/10.12688/f1000research.8800.1.

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Mechanotransduction is the process through which cells survey the mechanical properties of their environment, convert these mechanical inputs into biochemical signals, and modulate their phenotype in response. These mechanical inputs, which may be encoded in the form of extracellular matrix stiffness, dimensionality, and adhesion, all strongly influence cell morphology, migration, and fate decisions. One mechanism through which cells on planar or pseudo-planar matrices exert tensile forces and interrogate microenvironmental mechanics is through stress fibers, which are bundles composed of actin filaments and, in most cases, non-muscle myosin II filaments. Stress fibers form a continuous structural network that is mechanically coupled to the extracellular matrix through focal adhesions. Furthermore, myosin-driven contractility plays a central role in the ability of stress fibers to sense matrix mechanics and generate tension. Here, we review the distinct roles that non-muscle myosin II plays in driving mechanosensing and focus specifically on motility. In a closely related discussion, we also describe stress fiber classification schemes and the differing roles of various myosin isoforms in each category. Finally, we briefly highlight recent studies exploring mechanosensing in three-dimensional environments, in which matrix content, structure, and mechanics are often tightly interrelated. Stress fibers and the myosin motors therein represent an intriguing and functionally important biological system in which mechanics, biochemistry, and architecture all converge.

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Petrof, B. J., A. M. Kelly, N. A. Rubinstein et A. I. Pack. « Effect of hypothyroidism on myosin heavy chain expression in rat pharyngeal dilator muscles ». Journal of Applied Physiology 73, n^o 1 (1 juillet 1992) : 179–87. http://dx.doi.org/10.1152/jappl.1992.73.1.179.

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Although the association between hypothyroidism and obstructive sleep apnea is well established, the effect of thyroid hormone deficiency on contractile proteins in pharyngeal dilator muscles responsible for maintaining upper airway patency is unknown. In the present study, the effects of hypothyroidism on myosin heavy chain (MHC) expression were examined in the sternohyoid, geniohyoid, and genioglossus muscles of adult rats (n = 20). The relative proportions of MHC isoforms present were determined using MHC-specific monoclonal antibodies and oligonucleotide probes. All control muscles showed a paucity of type I MHC fibers, with greater than 90% of fibers containing fast-twitch type II MHCs. In the genioglossus muscle, a population of non-IIa non-IIb fast-twitch type II fibers (putatively identified as type IIx MHC fibers) were detected. Hypothyroidism induced significant changes in MHC expression in all muscles studied. In the sternohyoid, type I fibers increased from 6.2 to 16.9%, whereas type IIa fibers increased from 25.9 to 30.7%. Type I fibers in the geniohyoid increased from 1.2 to 12.8%, whereas type IIa fibers increased from 34.1 to 42.7%. The genioglossus showed the smallest relative increase in type I expression but the greatest induction of type IIa MHC. None of the muscles examined demonstrated reinduction of embryonic or neonatal MHC in response to thyroid hormone deficiency. In summary, hypothyroidism alters the MHC profile of pharyngeal dilators in a muscle-specific manner. These changes may play a role in the pathogenesis of obstructive apnea in hypothyroid patients.

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Jana, Siddhartha S., Kye-Young Kim, Jian Mao, Sachiyo Kawamoto, James R. Sellers et Robert S. Adelstein. « An Alternatively Spliced Isoform of Non-muscle Myosin II-C Is Not Regulated by Myosin Light Chain Phosphorylation ». Journal of Biological Chemistry 284, n^o 17 (23 février 2009) : 11563–71. http://dx.doi.org/10.1074/jbc.m806574200.

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Habicht, Juri, Ashley Mooneyham, Asumi Hoshino, Mihir Shetty, Xiaonan Zhang, Edith Emmings, Qing Yang, Courtney Coombes, Melissa K. Gardner et Martina Bazzaro. « UNC-45A breaks the microtubule lattice independently of its effects on non-muscle myosin II ». Journal of Cell Science 134, n^o 1 (1 décembre 2020) : jcs248815. http://dx.doi.org/10.1242/jcs.248815.

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ABSTRACTIn invertebrates, UNC-45 regulates myosin stability and functions. Vertebrates have two distinct isoforms of the protein: UNC-45B, expressed in muscle cells only, and UNC-45A, expressed in all cells and implicated in regulating both non-muscle myosin II (NMII)- and microtubule (MT)-associated functions. Here, we show that, in vitro and in human and rat cells, UNC-45A binds to the MT lattice, leading to MT bending, breakage and depolymerization. Furthermore, we show that UNC-45A destabilizes MTs independent of its C-terminal NMII-binding domain and even in the presence of the NMII inhibitor blebbistatin. These findings identified UNC-45A as a novel type of MT-severing protein with a dual non-mutually exclusive role in regulating NMII activity and MT stability. Because many human diseases, from cancer to neurodegenerative diseases, are caused by or associated with deregulation of MT stability, our findings have profound implications in the biology of MTs, as well as the biology of human diseases and possible therapeutic implications for their treatment.This article has an associated First Person interview with the joint first authors of the paper.

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Singh, Kuldeep, Anne B. Kim et Kathleen G. Morgan. « Non‐muscle myosin II regulates aortic stiffness through effects on specific focal adhesion proteins and the non‐muscle cortical cytoskeleton ». Journal of Cellular and Molecular Medicine 25, n^o 5 (6 février 2021) : 2471–83. http://dx.doi.org/10.1111/jcmm.16170.

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Chen, Ping, De-qiang Xu, Sheng-li Xu, He Xiao, Sheng-hong Wan, Xing-huan Wang, Michael E. DiSanto et Xin-hua Zhang. « Blebbistatin modulates prostatic cell growth and contrapctility through myosin II signaling ». Clinical Science 132, n^o 20 (19 octobre 2018) : 2189–205. http://dx.doi.org/10.1042/cs20180294.

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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 LC17a/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 LC17a, 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.

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Aguilar-Cuenca, Rocío, Clara Llorente-González, Jessica R. Chapman, Vanessa C. Talayero, Marina Garrido-Casado, Cristina Delgado-Arévalo, María Millán-Salanova et al. « Tyrosine Phosphorylation of the Myosin Regulatory Light Chain Controls Non-muscle Myosin II Assembly and Function in Migrating Cells ». Current Biology 30, n^o 13 (juillet 2020) : 2446–58. http://dx.doi.org/10.1016/j.cub.2020.04.057.

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Wendt, T., D. Taylor, K. Trybus et K. Taylor. « 3-D Electron Crystallography Reveals the “Off” State of Smooth Muscle Myosin. » Microscopy and Microanalysis 6, S2 (août 2000) : 86–87. http://dx.doi.org/10.1017/s143192760003292x.

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The activity of myosin II from vertebrate smooth and non-muscle cells is controlled by phosphorylation of the regulatory light chain (RLC). Smooth muscle heavy meromyosin (HMM) is a truncated double-headed myosin molecule that is soluble at physiological ionic strength. Subfragments of myosin containing two heads retain phosphorylation dependent regulation but single headed subfragments do not and are always “In”(Cremo et al., 1995; Trybus et al., 1997) thereby implicating head-head interactions as a fundamental feature of regulation. We have used a positively charged lipid monolayer to obtain 2-D crystalline arrays of both the unphosphorylated, inactive form (I-form) and thiophosphorylated, activated form (P-form) from chicken gizzard smooth muscle HMM obtained from a Baculovirus expression system.A comparison of averaged 2-D projections of both forms in negative stain at 2.3 nm resolution reveals distinct structural differences (Wendt et al., 1999). The two crystals have p2 symmetry but vastly different unit cell dimensions.

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Zeng, Q., D. Lagunoff, R. Masaracchia, Z. Goeckeler, G. Cote et R. Wysolmerski. « Endothelial cell retraction is induced by PAK2 monophosphorylation of myosin II ». Journal of Cell Science 113, n^o 3 (1 février 2000) : 471–82. http://dx.doi.org/10.1242/jcs.113.3.471.

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The p21-activated kinase (PAK) family includes several enzyme isoforms regulated by the GTPases Rac1 and Cdc42. PAK1, found in brain, muscle and spleen, has been implicated in triggering cytoskeletal rearrangements such as the dissolution of stress fibers and reorganization of focal complexes. The role of the more widely distributed PAK2 in controlling the cytoskeleton has been less well studied. Previous work has demonstrated that PAK2 can monophosphorylate the myosin II regulatory light chain and induce retraction of permeabilized endothelial cells. In this report we characterize PAK2's morphological and biochemical effect on intact endothelial cells utilizing microinjection of constitutively active PAK2. Under these conditions we observed a modification of the actin cytoskeleton with retraction of endothelial cell margins accompanied by an increase in monophosphorylation of myosin II. Selective inhibitors were used to analyze the mechanism of action of PAK2. Staurosporine, a direct inhibitor of PAK2, largely prevented the action of microinjected PAK2 in endothelial cells. Butanedione monoxime, a non-specific myosin ATPase inhibitor, also inhibited the effects of PAK2 implicating myosin in the changes in cytoskeletal reorganization. In contrast, KT5926, a specific inhibitor of myosin light chain kinase was ineffective in preventing the changes in morphology and the actin cytoskeleton. The additional finding that endogenous PAK2 associates with myosin II is consistent with the proposal that cell retraction and cytoskeletal rearrangements induced by microinjected PAK2 depend on the direct activation of myosin II by PAK2 monophosphorylation of the regulatory light chain.

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