Even-Ram, S. et al. Myosin IIA regulates cell motility and actomyosin-microtubule crosstalk. Nature Cell Biol. 9, 299-309

Craniofacial Developmental Biology and Regeneration Branch, National Institute of Dental and Craniofacial Research (NIDCR), National Institutes of Health, Bethesda, MD 20892, USA.
Nature Cell Biology (Impact Factor: 19.68). 04/2007; 9(3):299-309. DOI: 10.1038/ncb1540
Source: PubMed


Non-muscle myosin II has diverse functions in cell contractility, cytokinesis and locomotion, but the specific contributions of its different isoforms have yet to be clarified. Here, we report that ablation of the myosin IIA isoform results in pronounced defects in cellular contractility, focal adhesions, actin stress fibre organization and tail retraction. Nevertheless, myosin IIA-deficient cells display substantially increased cell migration and exaggerated membrane ruffling, which was dependent on the small G-protein Rac1, its activator Tiam1 and the microtubule moter kinesin Eg5. Myosin IIA deficiency stabilized microtubules, shifting the balance between actomyosin and microtubules with increased microtubules in active membrane ruffles. When microtubule polymerization was suppressed, myosin IIB could partially compensate for the absence of the IIA isoform in cellular contractility, but not in cell migration. We conclude that myosin IIA negatively regulates cell migration and suggest that it maintains a balance between the actomyosin and microtubule systems by regulating microtubule dynamics.

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Available from: Sharona Even-Ram, Oct 13, 2015
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    • "Nonmuscle myosin is the motor protein which slides actin filaments [20]. The activity of nonmuscle myosin is needed for cell motility, kariokinesis and trafficking of intracellular vesicles and these functions of nonmuscle myosin have been extensively studied [21], [22], [23], [24], [25], [26], [27], [28]. There are three isoforms of nonmuscle myosin, but isoforms IIA and IIB are the most abundant in cells. "
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    ABSTRACT: Type I collagen is extracellular matrix protein composed of two α1(I) and one α2(I) polypeptides that fold into triple helix. Collagen polypeptides are translated in coordination to synchronize the rate of triple helix folding to the rate of posttranslational modifications of individual polypeptides. This is especially important in conditions of high collagen production, like fibrosis. It has been assumed that collagen mRNAs are targeted to the membrane of the endoplasmic reticulum (ER) after translation of the signal peptide and by signal peptide recognition particle (SRP). Here we show that collagen mRNAs associate with the ER membrane even when translation is inhibited. Knock down of LARP6, an RNA binding protein which binds 5' stem-loop of collagen mRNAs, releases a small amount of collagen mRNAs from the membrane. Depolimerization of nonmuscle myosin filaments has a similar, but stronger effect. In the absence of LARP6 or nonmuscle myosin filaments collagen polypeptides become hypermodified, are poorly secreted and accumulate in the cytosol. This indicates lack of coordination of their synthesis and retro-translocation due to hypermodifications and misfolding. Depolimerization of nonmuscle myosin does not alter the secretory pathway through ER and Golgi, suggesting that the role of nonmuscle myosin is primarily to partition collagen mRNAs to the ER membrane. We postulate that collagen mRNAs directly partition to the ER membrane prior to synthesis of the signal peptide and that LARP6 and nonmuscle myosin filaments mediate this process. This allows coordinated initiation of translation on the membrane bound collagen α1(I) and α2(I) mRNAs, a necessary step for proper synthesis of type I collagen.
    PLoS ONE 10/2014; 9(10):e108870. DOI:10.1371/journal.pone.0108870 · 3.23 Impact Factor
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    • "Depletion of myosin IIA in carcinoma cell lines using siRNA decreased the number of stress fibers and focal adhesions and increased the rate of cell migration in a wound-healing assay [Sandquist et al., 2006]. Myosin IIA ablation in ES cells resulted in a marked decrease in contractility and an increase in cell migration velocity [Even-Ram et al., 2007]. RNAi experiments show that myosin IIA appears to function as the key negative regulator of cell spreading whereas myosin IIB depletion has little effect on spreading [Cai et al., 2006]. "
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    ABSTRACT: The actin cytoskeleton, which regulates cell polarity, adhesion, and migration, can influence cancer progression, including initial acquisition of malignant properties by normal cells, invasion of adjacent tissues, and metastasis to distant sites. Actin-dependent molecular motors, myosins, play key roles in regulating tumor progression and metastasis. In this review, we examine how non-muscle myosins regulate neoplastic transformation and cancer cell migration and invasion. Members of the myosin superfamily can act as either enhancers or suppressors of tumor progression. This review summarizes the current state of knowledge on how mutations or epigenetic changes in myosin genes and changes in myosin expression may affect tumor progression and patient outcomes and discusses the proposed mechanisms linking myosin inactivation or upregulation to malignant phenotype, cancer cell migration, and metastasis. © 2014 Wiley Periodicals, Inc.
    Cytoskeleton 08/2014; 71(8). DOI:10.1002/cm.21187 · 3.12 Impact Factor
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    • "These collective results of different studies on Cdc42- or Rac1-specific activation in response to BBS treatment might reflect species- or cell type–specific differences. The BBS-stimulated expansion of microtubules might partially explain the specificity of BBS-induced Rho GTPase activation [38], [39]. The interaction of a GEF(s) with microtubules and its subsequent translocation to the correct area might determine which Rho GTPase would be activated in that area. "
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    ABSTRACT: Non-muscle myosin II (NM II) regulates a wide range of cellular functions, including neuronal differentiation, which requires precise spatio-temporal activation of Rho GTPases. The molecular mechanism underlying the NM II-mediated activation of Rho GTPases is poorly understood. The present study explored the possibility that NM II regulates neuronal differentiation, particularly morphological changes in growth cones and the distal axon, through guanine nucleotide exchange factors (GEFs) of the Dbl family. NM II colocalized with GEFs, such as βPIX, kalirin and intersectin, in growth cones. Inactivation of NM II by blebbistatin (BBS) led to the increased formation of short and thick filopodial actin structures at the periphery of growth cones. In line with these observations, FRET analysis revealed enhanced Cdc42 activity in BBS-treated growth cones. BBS treatment also induced aberrant targeting of various GEFs to the distal axon where GEFs were seldom observed under physiological conditions. As a result, numerous protrusions and branches were generated on the shaft of the distal axon. The disruption of the NM II-GEF interactions by overexpression of the DH domains of βPIX or Tiam1, or by βPIX depletion with specific siRNAs inhibited growth cone formation and induced slender axons concomitant with multiple branches in cultured hippocampal neurons. Finally, stimulation with nerve growth factor induced transient dissociation of the NM II-GEF complex, which was closely correlated with the kinetics of Cdc42 and Rac1 activation. Our results suggest that NM II maintains proper morphology of neuronal growth cones and the distal axon by regulating actin dynamics through the GEF-Rho GTPase signaling pathway.
    PLoS ONE 04/2014; 9(4):e95212. DOI:10.1371/journal.pone.0095212 · 3.23 Impact Factor
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