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Spudich JA, Sivaramakrishnan S. Myosin VI: an innovative motor that challenged the swinging lever arm hypothesis. Nat Rev Mol Cell Biol 2010; 11:128-37. [PMID: 20094053 DOI: 10.1038/nrm2833] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The swinging crossbridge hypothesis states that energy from ATP hydrolysis is transduced to mechanical movement of the myosin head while bound to actin. The light chain-binding region of myosin is thought to act as a lever arm that amplifies movements near the catalytic site. This model has been challenged by findings that myosin VI takes larger steps along actin filaments than early interpretations of its structure seem to allow. We now know that myosin VI does indeed operate by an unusual approximately 180 degrees lever arm swing and achieves its large step size using special structural features in its tail domain.
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Affiliation(s)
- James A Spudich
- Department of Biochemistry, B400 Beckman Center, Stanford University School of Medicine, Stanford, California 94305-5307, USA.
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Abstract
Although myosin VI has properties that would allow it to function optimally as a dimer, full-length myosin VI exists as a monomer in isolation. Based on the ability of myosin VI monomers to dimerize when held in close proximity, we postulated that cargo binding normally regulates dimerization of myosin VI. We tested this hypothesis by expressing a known dimeric cargo adaptor protein of myosin VI, optineurin, and the myosin VI-binding segment from a monomeric cargo adaptor protein, Dab2. In the presence of these adaptor proteins, full-length myosin VI has ATPase properties of a dimer, appears as a dimer in electron micrographs, and moves processively on actin filaments. The results support a model in which cargo binding exposes internal dimerization sequences within full-length myosin VI. Because, unexpectedly, a monomeric fragment of Dab2 triggers dimerization, it would appear that myosin VI is designed to function as a dimer in cells.
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Blaine J, Okamura K, Giral H, Breusegem S, Caldas Y, Millard A, Barry N, Levi M. PTH-induced internalization of apical membrane NaPi2a: role of actin and myosin VI. Am J Physiol Cell Physiol 2009; 297:C1339-46. [PMID: 19776390 DOI: 10.1152/ajpcell.00260.2009] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Parathyroid hormone (PTH) plays a critical role in the regulation of renal phosphorous homeostasis by altering the levels of the sodium-phosphate cotransporter NaPi2a in the brush border membrane (BBM) of renal proximal tubular cells. While details of the molecular events of PTH-induced internalization of NaPi2a are emerging, the precise events governing NaPi2a removal from brush border microvilli in response to PTH remain to be fully determined. Here we use a novel application of total internal reflection fluorescence microscopy to examine how PTH induces movement of NaPi2a out of brush border microvilli in living cells in real time. We show that a dynamic actin cytoskeleton is required for NaPi2a removal from the BBM in response to PTH. In addition, we demonstrate that a myosin motor that has previously been shown to be coregulated with NaPi2a, myosin VI, is necessary for PTH-induced removal of NaPi2a from BBM microvilli.
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Affiliation(s)
- Judith Blaine
- Department of Medicine, University of Colorado Denver, Aurora, 80045, USA.
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Woolner S, Bement WM. Unconventional myosins acting unconventionally. Trends Cell Biol 2009; 19:245-52. [PMID: 19406643 DOI: 10.1016/j.tcb.2009.03.003] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2009] [Revised: 03/26/2009] [Accepted: 03/27/2009] [Indexed: 11/26/2022]
Abstract
Unconventional myosins are proteins that bind actin filaments in an ATP-regulated manner. Because of their association with membranes, they have traditionally been viewed as motors that function primarily to transport membranous organelles along actin filaments. Recently, however, a wealth of roles for myosins that are not obviously related to organelle transport have been uncovered, including organization of F-actin, mitotic spindle regulation and gene transcription. Furthermore, it has also become apparent that the motor domains of different myosins vary strikingly in their biophysical attributes. We suggest that the assumption that most unconventional myosins function primarily as organelle transporters might be misguided.
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Affiliation(s)
- Sarah Woolner
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester, UK.
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Kreft M, Potokar M, Stenovec M, Pangrsic T, Zorec R. Regulated exocytosis and vesicle trafficking in astrocytes. Ann N Y Acad Sci 2009; 1152:30-42. [PMID: 19161374 DOI: 10.1111/j.1749-6632.2008.04005.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Astrocytes are increasingly viewed as crucial cells supporting and integrating brain functions. It is thought that the release of gliotransmitters into the extracellular space by regulated exocytosis supports a significant part of communication between astrocytes and neurons. Prior to exocytosis, the membrane-bound vesicles are transported through the astrocyte cytoplasm. Our recent studies have revealed new insights into vesicle trafficking in the cytoplasm of astrocytes and are reviewed in this article. The prefusion mobility of fluorescently labeled peptidergic vesicles was studied in cultured rat and mouse astrocytes. Vesicle delivery to the plasma membrane involved an interaction with the cytoskeleton, in particular with microtubules and actin filaments. Interestingly, vesicle mobility in mouse astrocytes deficient in intermediate filaments show impaired directionality of peptidergic vesicle mobility. To explore whether stimuli that increase the concentration of free calcium ions in the cytoplasm triggered vesicular ATP release from astrocytes, human embryonic kidney-293T cells transfected with a P2X(3) receptor were used as sniffers to detect ATP release. Glutamate stimulation of astrocytes was followed by an increase in the incidence of small, transient, inward currents in sniffer cells, reminiscent of postsynaptic quantal events observed at synapses. Some of the membrane-bound vesicles are retrieved from the plasma membrane to be recycled back into the cytosol. Trafficking velocity of postfusion (recycling) atrial natriuretic peptide vesicles was one order of magnitude slower in comparison to the mobility of prefusion vesicles. However, transport of all vesicle types studied required an intact cytoskeleton.
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Affiliation(s)
- Marko Kreft
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana and Celica Biomedical Center, Ljubljana, Slovenia
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56
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Hertzano R, Shalit E, Rzadzinska AK, Dror AA, Song L, Ron U, Tan JT, Shitrit AS, Fuchs H, Hasson T, Ben-Tal N, Sweeney HL, de Angelis MH, Steel KP, Avraham KB. A Myo6 mutation destroys coordination between the myosin heads, revealing new functions of myosin VI in the stereocilia of mammalian inner ear hair cells. PLoS Genet 2008; 4:e1000207. [PMID: 18833301 PMCID: PMC2543112 DOI: 10.1371/journal.pgen.1000207] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Accepted: 08/25/2008] [Indexed: 11/18/2022] Open
Abstract
Myosin VI, found in organisms from Caenorhabditis elegans to humans, is essential for auditory and vestibular function in mammals, since genetic mutations lead to hearing impairment and vestibular dysfunction in both humans and mice. Here, we show that a missense mutation in this molecular motor in an ENU-generated mouse model, Tailchaser, disrupts myosin VI function. Structural changes in the Tailchaser hair bundles include mislocalization of the kinocilia and branching of stereocilia. Transfection of GFP-labeled myosin VI into epithelial cells and delivery of endocytic vesicles to the early endosome revealed that the mutant phenotype displays disrupted motor function. The actin-activated ATPase rates measured for the D179Y mutation are decreased, and indicate loss of coordination of the myosin VI heads or ‘gating’ in the dimer form. Proper coordination is required for walking processively along, or anchoring to, actin filaments, and is apparently destroyed by the proximity of the mutation to the nucleotide-binding pocket. This loss of myosin VI function may not allow myosin VI to transport its cargoes appropriately at the base and within the stereocilia, or to anchor the membrane of stereocilia to actin filaments via its cargos, both of which lead to structural changes in the stereocilia of myosin VI–impaired hair cells, and ultimately leading to deafness. Human deafness is extremely heterogeneous, with mutations in over 50 genes known to be associated with this common form of sensory loss. Among them, mutations in five myosins are associated with human hereditary hearing impairment, demonstrating that this family of proteins is essential for the proper function of the inner ear. Myosins, motor proteins found in eukaryotic cells, are responsible for actin-based motility. Composed of a motor domain and a tail, the former binds filamentous actin and uses ATP hydrolysis to generate force and move along the filaments, while the latter binds to cargos in the cell. Myosin VI is unique among myosins due to its movement along actin towards the minus or pointed end, rather than the positive or barbed end. Mutations in this myosin are associated with human deafness. Much of our information regarding myosin VI comes from studies in cell culture or mouse mutants with mutations leading to deafness. Here, we describe a deaf mouse mutant, Tailchaser, with a mutation in myosin VI. Our data describe new functions for myosin VI in the hair cells of the inner ear, showing how alterations in this motor can lead to a human sensory disorder.
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MESH Headings
- Adenosine Triphosphatases/genetics
- Adenosine Triphosphatases/metabolism
- Animals
- Cell Line
- Chromosome Mapping
- Deafness/genetics
- Deafness/metabolism
- Female
- Hair Cells, Auditory, Inner/chemistry
- Hair Cells, Auditory, Inner/metabolism
- Humans
- Male
- Mice
- Mice, Inbred C3H
- Mice, Inbred C57BL
- Mice, Knockout
- Models, Molecular
- Mutation, Missense
- Myosin Heavy Chains/chemistry
- Myosin Heavy Chains/genetics
- Myosin Heavy Chains/metabolism
- Protein Structure, Tertiary
- Protein Transport
- Transport Vesicles/chemistry
- Transport Vesicles/metabolism
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Affiliation(s)
- Ronna Hertzano
- Department of Human Molecular Genetics and Biochemistry, Tel Aviv University, Tel Aviv, Israel
| | - Ella Shalit
- Department of Human Molecular Genetics and Biochemistry, Tel Aviv University, Tel Aviv, Israel
| | - Agnieszka K. Rzadzinska
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Amiel A. Dror
- Department of Human Molecular Genetics and Biochemistry, Tel Aviv University, Tel Aviv, Israel
| | - Lin Song
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Uri Ron
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Joshua T. Tan
- Section of Cell and Developmental Biology, University of California San Diego, La Jolla, California, United States of America
| | | | - Helmut Fuchs
- Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Experimental Genetics, Neuherberg, Germany
| | - Tama Hasson
- Section of Cell and Developmental Biology, University of California San Diego, La Jolla, California, United States of America
| | - Nir Ben-Tal
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - H. Lee Sweeney
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Martin Hrabe de Angelis
- Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Experimental Genetics, Neuherberg, Germany
- Technical University of Munich, Munich, Germany
| | - Karen P. Steel
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Karen B. Avraham
- Department of Human Molecular Genetics and Biochemistry, Tel Aviv University, Tel Aviv, Israel
- * E-mail:
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Spatiotemporal analysis of endocytosis and membrane distribution of fluorescent sterols in living cells. Histochem Cell Biol 2008; 130:891-908. [DOI: 10.1007/s00418-008-0488-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/30/2008] [Indexed: 01/04/2023]
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58
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Kakigi A, Okada T, Takeda T, Taguchi D, Nishioka R, Nishimura M. Actin filaments and microtubules regulate endocytosis in marginal cells of the stria vascularis. Acta Otolaryngol 2008; 128:856-60. [PMID: 18608006 DOI: 10.1080/00016480701777373] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
CONCLUSION Cationized ferritin (CF) was internalized via clathrin-mediated endocytosis. This process depends on clathrin, actin filaments, and microtubules. Microperoxidase (MPO) was internalized via a clathrin- and caveolin-independent endocytic pathway, which was partially dependent on microtubules but independent of clathrin and actin filaments. OBJECTIVE We investigated the role of actin filaments and microtubules in the transport of endocytic carrier vesicles (ECVs) from the plasma membrane to the early sorting endosomes, using CF and MPO as tracers. MATERIALS AND METHODS Fifty-five guinea pigs were used. The animals were divided into a CF endocytosis group and an MPO endocytosis group. These groups consisted of control, nocodazole-treated, cytochalasin (Cyt D)-treated, Cyt D + nocodazole-treated, and geldanamycin-treated subgroups. RESULTS For CF endocytosis, the following results were obtained. In the nocodazole experiment, in which microtubules were disrupted to form monomeric tubulin, the number of ECVs loaded with CF was greatly decreased. In the Cyt D experiment, in which the actin filaments were disrupted to form monomers, the number of ECVs labeled with CF was also greatly decreased. In the geldanamycin experiment, in which clathrin-mediated endocytosis was regulated and actin stress fibers were dissolved, the endocytosis of CF was severely inhibited. For MPO endocytosis, in the nocodazole experiment, the endocytosis of MPO was markedly suppressed.
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59
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Iwaki M, Iwane AH, Ikebe M, Yanagida T. Biased Brownian motion mechanism for processivity and directionality of single-headed myosin-VI. Biosystems 2008; 93:39-47. [DOI: 10.1016/j.biosystems.2008.03.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2008] [Revised: 03/19/2008] [Accepted: 03/24/2008] [Indexed: 11/30/2022]
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Altman D, Goswami D, Hasson T, Spudich JA, Mayor S. Precise positioning of myosin VI on endocytic vesicles in vivo. PLoS Biol 2008; 5:e210. [PMID: 17683200 PMCID: PMC1939883 DOI: 10.1371/journal.pbio.0050210] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2006] [Accepted: 06/07/2007] [Indexed: 11/19/2022] Open
Abstract
Myosin VI has been studied in both a monomeric and a dimeric form in vitro. Because the functional characteristics of the motor are dramatically different for these two forms, it is important to understand whether myosin VI heavy chains are brought together on endocytic vesicles. We have used fluorescence anisotropy measurements to detect fluorescence resonance energy transfer between identical fluorophores (homoFRET) resulting from myosin VI heavy chains being brought into close proximity. We observed that, when associated with clathrin-mediated endocytic vesicles, myosin VI heavy chains are precisely positioned to bring their tail domains in close proximity. Our data show that on endocytic vesicles, myosin VI heavy chains are brought together in an orientation that previous in vitro studies have shown causes dimerization of the motor. Our results are therefore consistent with vesicle-associated myosin VI existing as a processive dimer, capable of its known trafficking function.
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Affiliation(s)
- David Altman
- Department of Biochemistry, Stanford University Medical Center, Stanford, California, United States of America
| | - Debanjan Goswami
- National Centre for Biological Sciences, UAS-GKVK Campus, Bangalore, India
| | - Tama Hasson
- Division of Biological Sciences, University of California San Diego, La Jolla, California, United States of America
| | - James A Spudich
- Department of Biochemistry, Stanford University Medical Center, Stanford, California, United States of America
- National Centre for Biological Sciences, UAS-GKVK Campus, Bangalore, India
- * To whom correspondence should be addressed. E-mail:
| | - Satyajit Mayor
- National Centre for Biological Sciences, UAS-GKVK Campus, Bangalore, India
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61
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Hosein RE, Gavin RH. Myo1 localizes to phagosomes, some of which traffic to the nucleus in a Myo1-dependent manner in Tetrahymena thermophila. ACTA ACUST UNITED AC 2008; 64:926-35. [PMID: 17688250 DOI: 10.1002/cm.20233] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Myo1 is one of 13 myosins in Tetrahymena thermophila. Initially, twelve of the myosins in Tetrahymena were assigned to Class XX in the myosin superfamily but recently re-assigned to a subclass within Class XIV. In a previous study, we reported that genomic knockout of MYO1 affected phagocytosis and macronuclear amitosis. These two phenotypes have appeared disparate because a possible mechanism linking phagocytosis and amitosis was unknown. In the present study, Myo1 localization was investigated in order to further link machinery for phagocytosis and amitosis. Antibodies directed against the Myo1 motor domain detected an immunospecific polypeptide at 175-180 kDa on immunoblots of wild-type proteins. The 175-180 kDa polypeptide was not detected on immunoblots of proteins from the knockout strain. For immunofluorescence microscopy, cells were allowed to internalize fluorescent beads as markers for phagosomes. In wild-type cells, anti-Myo1 and anti-actin antibodies co-localized to the periphery of phagosomes and the macronucleus. In the MYO1-knockout strain only background fluorescence was observed with anti-Myo1 antibody. Confocal x-z series through macronuclei revealed fluorescent beads within the nucleoplasm. Statistical analysis showed a significant difference between the mean distributions of fluorescent beads in the nucleoplasm of wild-type and MYO1-knockout cells. A fluorescent dye was used to label plasma membrane in living cells. Dye-labeled vacuoles trafficked to the macronucleus. Trafficking of phagosomes to the macronucleus in a myosin-dependent manner is a novel finding and a possible mechanism for targeting myosin and actin to the nucleus.
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Affiliation(s)
- Roland E Hosein
- Department of Biology, Brooklyn College of the City University of New York, Brooklyn 11210, New York, USA
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62
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Abstract
In polarized epithelial cells such as those that line the inner ear, kidney and gut, myosin VI has been localized to the intermicrovillar domains where it is proposed to regulate clathrin-dependent endocytosis; however, a direct role for myosin VI in apical endocytosis has not been shown. We examined the apical membrane distribution and endocytosis of cystic fibrosis transmembrane conductance regulator (CFTR) in myosin VI-deficient Snell's Waltzer Myo6((sv/sv)) mice. Confocal microscopy and cell-surface biotinylation confirmed that surface levels of CFTR in the intestine of Myo6((sv/sv)) mice were markedly higher, and CFTR internalization from the apical plasma membrane was reduced compared with heterozygous controls. Consistent with a defect in CFTR endocytosis and accumulation at the cell surface, exaggerated CFTR-mediated fluid secretion was observed in Myo6((sv/sv)) mice following treatment of isolated jejunum with the cyclic GMP-activated heat stable enterotoxin. These data establish that myosin VI modulates apical endocytosis and may be an important physiological modulator of CFTR function and CFTR-associated secretory diarrhea in the gut.
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Affiliation(s)
- Nadia Ameen
- Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
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63
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Watanabe TM, Higuchi H. Stepwise movements in vesicle transport of HER2 by motor proteins in living cells. Biophys J 2007; 92:4109-20. [PMID: 17369416 PMCID: PMC1868978 DOI: 10.1529/biophysj.106.094649] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The stepwise movements generated by myosin, dynein, and kinesin were observed in living cells in an attempt to understand the molecular mechanisms of movement within cells. First, the sequential process of the transport of vesicles, including human epidermal factor 2 receptor, after endocytosis was observed for long periods in three dimensions using quantum dots (QDs) and a three-dimensional confocal microscope. QD vesicles, after being endocytosed into the cells, moved along the membrane by transferring actin filaments and were then rapidly transported toward the nucleus along microtubules. Second, the position of vesicles was detected with a precision up to 1.9 nm and 330 micros using a new two-dimensional tracking method. The movement of the QDs transported by myosin VI lying just beneath the cell membrane consisted of 29- and 15-nm steps with a transition phase between these two steps. QD vesicles were then transported toward the nucleus or away from the nucleus toward the cell membrane with successive 8-nm steps. The stepwise movements of these motor proteins in cells were observed using new imaging methods that allowed the molecular mechanisms underlying traffic to and from the membrane to be determined.
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Affiliation(s)
- Tomonobu M Watanabe
- Biomedical and Engineering Research Organization, Tohoku University, Sendai, Japan
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64
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Tada H, Higuchi H, Wanatabe TM, Ohuchi N. In vivo real-time tracking of single quantum dots conjugated with monoclonal anti-HER2 antibody in tumors of mice. Cancer Res 2007; 67:1138-44. [PMID: 17283148 DOI: 10.1158/0008-5472.can-06-1185] [Citation(s) in RCA: 289] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Studies with tracking of single nanoparticles are providing new insights into the interactions and processes involved in the transport of drug carriers in living mice. Here, we report the tracking of a single particle quantum dot (Qdot) conjugated with tumor-targeting antibody in tumors of living mice using a dorsal skinfold chamber and a high-speed confocal microscope with a high-sensitivity camera. Qdot labeled with the monoclonal anti-HER2 antibody was injected into mice with HER2-overexpressing breast cancer to analyze the molecular processes of its mechanistic delivery to the tumor. Movement of single complexes of the Qdot-antibody could be clearly observed at 30 frames/s inside the tumor through a dorsal skinfold chamber. We successfully identified six processes of delivery: initially in the circulation within a blood vessel, during extravasation, in the extracelullar region, binding to HER2 on the cell membrane, moving from the cell membrane to the perinuclear region, and in the perinuclear region. The six processes were quantitatively analyzed to understand the rate-limiting constraints on Qdot-antibody delivery. The movement of the complexes at each stage was "stop-and-go." The image analysis of the delivery processes of single particles in vivo provides valuable information on antibody-conjugated therapeutic nanoparticles, which will be useful in increasing therapeutic efficacy.
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Affiliation(s)
- Hiroshi Tada
- Division of Surgical Oncology, Graduate School of Medicine and Biomedical Engineering Research Organization, Tohoku University, 6-6-11 Aramaki, Sendai, Miyagi 980-8578, Japan
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Affiliation(s)
- Beatrice Knudsen
- Fred Hutchinson Cancer Research Center, Program in Cancer Biology, Division of Public Health Sciences, 1100 Fairview Avenue North, M5-A864, Seattle, WA 98109, USA.
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66
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Sweeney HL, Houdusse A. What can myosin VI do in cells? Curr Opin Cell Biol 2006; 19:57-66. [PMID: 17175153 DOI: 10.1016/j.ceb.2006.12.005] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2006] [Accepted: 12/07/2006] [Indexed: 11/27/2022]
Abstract
The recently solved structure of the myosin VI motor demonstrates that the unique insert at the end of the motor is responsible for the reversal of the normal myosin directionality. A second class-specific insert near the nucleotide-binding pocket contributes to myosin VI's unique kinetic tuning, allowing it to function either as an actin-based transporter or as an anchoring protein. Recent biochemical and biophysical studies have shown that the native molecule can form dimers upon clustering, and cell biological studies have demonstrated that it clearly does play both transport and anchoring roles in cells. These mechanistic insights allow us to speculate on how unusual aspects of myosin VI structure and function allow it to fill unique niches in cells.
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Affiliation(s)
- H Lee Sweeney
- Department of Physiology University of Pennsylvania School of Medicine, 3700 Hamilton Walk, Philadelphia, PA 19104-6085 USA.
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67
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Piehl M, Lehmann C, Gumpert A, Denizot JP, Segretain D, Falk MM. Internalization of large double-membrane intercellular vesicles by a clathrin-dependent endocytic process. Mol Biol Cell 2006; 18:337-47. [PMID: 17108328 PMCID: PMC1783799 DOI: 10.1091/mbc.e06-06-0487] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Beyond its well-documented role in vesicle endocytosis, clathrin has also been implicated in the internalization of large particles such as viruses, pathogenic bacteria, and even latex beads. We have discovered an additional clathrin-dependent endocytic process that results in the internalization of large, double-membrane vesicles at lateral membranes of cells that are coupled by gap junctions (GJs). GJ channels bridge apposing cell membranes to mediate the direct transfer of electrical currents and signaling molecules from cell to cell. Here, we report that entire GJ plaques, clusters of GJ channels, can be internalized to form large, double-membrane vesicles previously termed annular gap junctions (AGJs). These internalized AGJ vesicles subdivide into smaller vesicles that are degraded by endo/lysosomal pathways. Mechanistic analyses revealed that clathrin-dependent endocytosis machinery-components, including clathrin itself, the alternative clathrin-adaptor Dab2, dynamin, myosin-VI, and actin are involved in the internalization, inward movement, and degradation of these large, intercellular double-membrane vesicles. These findings contribute to the understanding of clathrin's numerous emerging functions.
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Affiliation(s)
- Michelle Piehl
- *Department of Biological Sciences, Lehigh University, Bethlehem, PA 18015
| | - Corinna Lehmann
- *Department of Biological Sciences, Lehigh University, Bethlehem, PA 18015
| | - Anna Gumpert
- *Department of Biological Sciences, Lehigh University, Bethlehem, PA 18015
| | - Jean-Pierre Denizot
- Unité de Neurosciences Intégratives et Computationnelles, Centre National de la Recherche Scientifique UPR 2191, Gif sur Yvette 91198 Cedex, France; and
| | - Dominique Segretain
- Institut National de la Santé et de la Recherche Médicale U670, Université de Paris 5, Paris, France
| | - Matthias M. Falk
- *Department of Biological Sciences, Lehigh University, Bethlehem, PA 18015
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Abstract
Early in evolution, the diversification of membrane-bound compartments that characterize eukaryotic cells was accompanied by the elaboration of molecular machineries that mediate intercompartmental communication and deliver materials to specific destinations. Molecular motors that move on tracks of actin filaments or microtubules mediate the movement of organelles and transport between compartments. The subjects of this review are the motors that power the transport steps along the endocytic and recycling pathways, their modes of attachment to cargo and their regulation.
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Affiliation(s)
- Thierry Soldati
- Départment de Biochimie, Faculté des Sciences, Université de Genève, 30 quai Ernest Ansermet, Sciences II, CH-1211-Genève-4, Switzerland.
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69
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Potokar M, Kreft M, Li L, Daniel Andersson J, Pangrsic T, Chowdhury HH, Pekny M, Zorec R. Cytoskeleton and Vesicle Mobility in Astrocytes. Traffic 2006; 8:12-20. [PMID: 17229312 DOI: 10.1111/j.1600-0854.2006.00509.x] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Exocytotic vesicles in astrocytes are increasingly viewed as essential in astrocyte-to-neuron communication in the brain. In neurons and excitable secretory cells, delivery of vesicles to the plasma membrane for exocytosis involves an interaction with the cytoskeleton, in particular microtubules and actin filaments. Whether cytoskeletal elements affect vesicle mobility in astrocytes is unknown. We labeled single vesicles with fluorescent atrial natriuretic peptide and monitored their mobility in rat astrocytes with depolymerized microtubules, actin, and intermediate filaments and in mouse astrocytes deficient in the intermediate filament proteins glial fibrillary acidic protein and vimentin. In astrocytes, as in neurons, microtubules participated in directional vesicle mobility, and actin filaments played an important role in this process. Depolymerization of intermediate filaments strongly affected vesicle trafficking and in their absence the fraction of vesicles with directional mobility was reduced.
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Affiliation(s)
- Maja Potokar
- Celica Biomedical Sciences Center, Stegne 21c, SI-1000 Ljubljana, Slovenia
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Naccache SN, Hasson T. Myosin VI altered at threonine 406 stabilizes actin filaments in vivo. ACTA ACUST UNITED AC 2006; 63:633-45. [PMID: 16917816 DOI: 10.1002/cm.20150] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Myosin VI is a minus-end directed actin-based molecular motor implicated in uncoated endocytic vesicle transport. Recent kinetic studies have shown that myosin VI displays altered ADP release kinetics under different load conditions allowing myosin VI to serve alternately as a transporter or as an actin tether. We theorized that one potential regulatory event to modulate between these kinetic choices is phosphorylation at a conserved site, threonine 406 (T406) in the myosin VI motor domain. Alterations mimicking the phosphorylated (T406E) and dephosphorylated state (T406A) were introduced into a GFP-myosin VI fusion (GFP-M6). Live cell imaging revealed that GFP-M6(T406E) expression changed the path myosin VI took in its transport of uncoated endocytic vesicles. Rather than routing vesicles inwards as seen in GFP-M6 and GFP-M6(T406A) expressing cells, GFP-M6(T406E) moved vesicles into clusters at distinct peripheral sites. GFP-M6(T406E) expression also increased the density of the actin cytoskeleton. Filaments were enriched at the vesicle cluster sites. This was not due to a gross redistribution of the actin polymerization machinery. Instead the filament density correlated to the fixed positioning of GFP-M6(T406E)-associated vesicles on F-actin, leading to inhibition of actin depolymerization. Our study suggests that phosphorylation at T406 changes the nature of myosin VI's interaction with actin in vivo.
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Affiliation(s)
- Samia N Naccache
- Section of Cell and Developmental Biology, Division of Biological Sciences, University of California at San Diego, La Jolla, California 92093, USA.
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71
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Kochubey O, Majumdar A, Klingauf J. Imaging Clathrin Dynamics in Drosophila melanogaster Hemocytes Reveals a Role for Actin in Vesicle Fission. Traffic 2006; 7:1614-27. [PMID: 17014698 DOI: 10.1111/j.1600-0854.2006.00492.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Clathrin-mediated endocytosis (CME) is essential for maintaining many basic cellular processes. We monitored the dynamics of clathrin in live Drosophila melanogaster hemocytes overexpressing clathrin light chain fused to enhanced green fluorescent protein (EGFP) using evanescent wave microscopy. Membrane-associated clathrin-coated structures (CCS) constitutively appeared at the peripheral filopodial membrane, moved centripetally while growing in intensity, before being eventually endocytosed within a few tens of seconds. This directed CCS traffic was independent of microtubules but could be blocked by latrunculin A. Taking advantage of available mutants of Drosophila, we expressed clathrin-EGFP in wasp and shibire mutant backgrounds to study the role of actin and dynamin in CCS dynamics and CME in hemocytes. We show that actin plays an essential role in CME in these cells, and that actin and dynamin act at the same stage, but independent of each other. Drosophila melanogaster hemocytes proved to be a promising model system to uncover the molecular events during CME in combining live-cell imaging and genetic analysis.
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Affiliation(s)
- Olexiy Kochubey
- Department of Membrane Biophysics, Max-Planck Institute for Biophysical Chemistry, D-37077 Goettingen, Germany
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72
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O'Connell CB, Tyska MJ, Mooseker MS. Myosin at work: motor adaptations for a variety of cellular functions. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1773:615-30. [PMID: 16904206 DOI: 10.1016/j.bbamcr.2006.06.012] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2006] [Revised: 05/22/2006] [Accepted: 06/30/2006] [Indexed: 12/30/2022]
Abstract
Cells have evolved multiple mechanisms to overcome the effects of entropy and diffusion to create a highly ordered environment. For cells to function properly, some components must be anchored to provide a framework or structure. Others must be rapidly transported over long distances to generate asymmetries in cell morphology and composition. To accomplish long-range transport, cells cannot rely on diffusion alone as many large organelles and macromolecular complexes are essentially immobilized by the dense meshwork of the cytosol. One strategy used by cells to overcome diffusion is to harness the free energy liberated by ATP hydrolysis through molecular motors. Myosins are a family of actin based molecular motors that have evolved a variety of ways to contribute to cellular organization through numerous modifications to the manner they convert that free energy into mechanical work.
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73
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Abstract
Myosin VI is an unconventional motor protein, and its mutation is responsible for the familiar conditions sensorineural deafness and hypertrophic cardiomyopathy. Myosin VI is found to play a key role in the protein trafficking and homeostasis of the Golgi complex. However, very little is known about how myosin VI is regulated and whether myosin VI has a function in the DNA damage response. Here, we found that myosin VI is regulated by DNA damage in a p53-dependent manner and possesses a novel function in the p53-dependent prosurvival pathway. Specifically, we show that myosin VI is induced by p53 and DNA damage in a p53-dependent manner. We found that p53 directly binds to, and activates, the promoter of the myosin VI gene. We also show that the intracellular localization of myosin VI is substantially altered by p53 and DNA damage in a p53-dependent manner such that the pool of myosin VI in endocytic vesicles, membrane ruffles, and cytosol migrates to the Golgi complex, perinuclear membrane, and nucleus. Furthermore, we show that knockdown of myosin VI attenuates activation of p53 and impairs Golgi complex integrity, which makes myosin VI-deficient cells susceptible to apoptosis upon DNA damage. Taken together, we found a novel function for p53 in the maintenance of Golgi complex integrity and for myosin VI in the p53-dependent prosurvival pathway.
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Affiliation(s)
- Eun Joo Jung
- Department of Cell Biology, MCLM 660, 1530 3rd Ave. S, Birmingham, AL 35294-0005, USA
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74
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Iwaki M, Tanaka H, Iwane AH, Katayama E, Ikebe M, Yanagida T. Cargo-binding makes a wild-type single-headed myosin-VI move processively. Biophys J 2006; 90:3643-52. [PMID: 16500969 PMCID: PMC1440745 DOI: 10.1529/biophysj.105.075721] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Class VI myosin is an intracellular vesicle and organelle transporter that moves along actin filaments in a direction opposite to most other known myosin classes. The myosin-VI was expected to form a dimer to move processively along actin filaments with a hand-over-hand mechanism like other myosin organelle transporters. Recently, however, wild-type myosin-VI was demonstrated to be monomer and single-headed, casting a doubt on its processivity. By using single molecule techniques, we show that green-fluorescent-protein-tagged single-headed, wild-type myosin-VI does not move processively. However, when coupled to 200-nm polystyrene beads (comparable to intracellular vesicles in size) at a ratio of one head per bead, single-headed myosin-VI moves processively with large (40-nm) steps. The characteristics of this monomer-driven movement were different to that of artificial dimer-driven movement: Compared to the artificial dimer, the monomer-bead complex had a reduced stall force (1 pN compared to 2 pN), an average run length 2.5-fold shorter (91 nm compared to 220 nm) and load-dependent step size. Furthermore, we found that a monomer-bead complex moved more processively in a high viscous solution (40-fold higher than water) similar to cellular environment. Because the diffusion constant of the bead is 60-fold lower than myosin-VI heads alone in water, we propose a model in which the bead acts as a diffusional anchor for the myosin-VI, enhancing its rebinding following detachment and supporting processive movement of the bead-monomer complexes. Although a single-headed myosin-VI was able to move processively with a large cargo, the travel distance was rather short. Multiple molecules may be involved in the cargo transport for a long travel distance in cells.
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Affiliation(s)
- Mitsuhiro Iwaki
- Department of Biophysical Engineering, Osaka University, Suita, Osaka, Japan
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75
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Fernandez-Borja M, Janssen L, Verwoerd D, Hordijk P, Neefjes J. RhoB regulates endosome transport by promoting actin assembly on endosomal membranes through Dia1. J Cell Sci 2005; 118:2661-70. [PMID: 15944396 DOI: 10.1242/jcs.02384] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rho GTPases are crucial regulators of the actin cytoskeleton and they play a role in the control of membrane trafficking. In contrast to the close family members RhoA and RhoC, RhoB localises to endosomes and delays epidermal growth factor receptor traffic. Here, we show that activated RhoB induces the peripheral distribution of endosomes, which align along subcortical actin stress fibres and are surrounded by an actin coat. The Diaphanous-related formin, Dia1, is recruited to endosomes by activated RhoB. Dia1 is required for the formation of the actin coat around endosomes downstream of RhoB, connecting membrane trafficking with the regulation of actin dynamics.
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76
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Abstract
The myosin family of actin filament-based molecular motors consists of at least 20 structurally and functionally distinct classes. The human genome contains nearly 40 myosin genes, encoding 12 of these classes. Myosins have been implicated in a variety of intracellular functions, including cell migration and adhesion; intracellular transport and localization of organelles and macromolecules; signal transduction; and tumor suppression. In this review, recent insights into the remarkable diversity in the mechanochemical and functional properties associated with this family of molecular motors are discussed.
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Affiliation(s)
- Mira Krendel
- Department of Molecular Biology, Yale University, New Haven, CN, USA.
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77
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Shetty RS, Bose SC, Nickell MD, McIntyre JC, Hardin DH, Harris AM, McClintock TS. Transcriptional changes during neuronal death and replacement in the olfactory epithelium. Mol Cell Neurosci 2005; 30:90-107. [PMID: 16027002 DOI: 10.1016/j.mcn.2005.06.003] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2005] [Revised: 06/10/2005] [Accepted: 06/13/2005] [Indexed: 11/30/2022] Open
Abstract
The olfactory epithelium has the unusual ability to replace its neurons. We forced replacement of mouse olfactory sensory neurons by bulbectomy. Microarray, bioinformatics, and in situ hybridization techniques detected a rapid shift in favor of pro-apoptotic proteins, a progressive immune response by macrophages and dendritic cells, and identified or predicted 439 mRNAs enriched in olfactory sensory neurons, including gene silencing factors and sperm flagellar proteins. Transcripts encoding cell cycle regulators, axonogenesis proteins, and transcription factors and signaling proteins that promote proliferation and differentiation were increased at 5--7 days after bulbectomy and were expressed by basal progenitor cells or immature neurons. The transcription factors included Nhlh 1, Hes 6, Lmyc 1, c-Myc, Mxd 4, Id 1, Nmyc 1, Cited 2, c-Myb, Mybl 1, Tead 2, Dp 1, Gata 2, Lmo 1, and Sox1 1. The data reveal significant similarities with embryonic neurogenesis and make several mechanistic predictions, including the roles of the transcription factors in the olfactory sensory neuron lineage.
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Affiliation(s)
- Ranjit S Shetty
- Department of Physiology, Cellular and Molecular Neuroscience of Sensory Systems Training Program, University of Kentucky, 800 Rose Street, Lexington, KY 40536-0298, USA
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78
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Yang LE, Maunsbach AB, Leong PKK, McDonough AA. Redistribution of myosin VI from top to base of proximal tubule microvilli during acute hypertension. J Am Soc Nephrol 2005; 16:2890-6. [PMID: 16107581 DOI: 10.1681/asn.2005040366] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
During acute hypertension, Na(+)/H(+) exchangers (NHE3) retract from top to base of proximal tubule microvilli (MV) and Na(+) reabsorption decreases in proximal tubule. This study aimed to determine whether the actin-based motor myosin VI coordinately retracts with NHE3 in response to acute hypertension. BP was raised approximately 50 mmHg in rats for 20 to 30 min or sham treated, and kidneys were analyzed by subcellular fractionation or microscopy. During acute hypertension, myosin VI redistributed from low density apical MV-enriched membranes (from 23 +/- 2.4 to 11.4 +/- 2.2%) into higher density membranes (from 23.2 +/- 0.7 to 36.9 +/- 2.6%). By confocal microscopy, myosin VI was detected over the whole length of the MV in controls, then became completely focused at the base of MV during acute hypertension. For electron microscopic analysis using immunogold labeling, MV were divided into five zones from top (z1) to base (z5). In controls, myosin VI was evenly distributed through the five MV zones. In acute hypertension, myosin VI decreased in z1 (from 20.6 +/- 1.9 to 10.5 +/- 2.3%) and z2 (from 21.0 +/- 2.0 to 13.2 +/- 1.4%) and increased in z5 (from 21.1 +/- 3.3 to 38.6 +/- 3.0%). These results provide the first observation that acute hypertension causes myosin VI redistribution and support the idea that myosin VI may serve as the molecular motor for NHE3 retraction from top to base of MV during acute hypertension.
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Affiliation(s)
- Li E Yang
- Department of Physiology and Biophysics, University of Southern California Keck School of Medicine, 1333 San Pablo Street, MMR 626, Los Angeles, CA 90089-9142, USA
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79
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Reed BC, Cefalu C, Bellaire BH, Cardelli JA, Louis T, Salamon J, Bloecher MA, Bunn RC. GLUT1CBP(TIP2/GIPC1) interactions with GLUT1 and myosin VI: evidence supporting an adapter function for GLUT1CBP. Mol Biol Cell 2005; 16:4183-201. [PMID: 15975910 PMCID: PMC1196329 DOI: 10.1091/mbc.e04-11-0978] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
We identified a novel interaction between myosin VI and the GLUT1 transporter binding protein GLUT1CBP(GIPC1) and first proposed that as an adapter molecule it might function to couple vesicle-bound proteins to myosin VI movement. This study refines the model by identifying two myosin VI binding domains in the GIPC1 C terminus, assigning respective oligomerization and myosin VI binding functions to separate N- and C-terminal domains, and defining a central region in the myosin VI tail that binds GIPC1. Data further supporting the model demonstrate that 1) myosin VI and GIPC1 interactions do not require a mediating protein; 2) the myosin VI binding domain in GIPC1 is necessary for intracellular interactions of GIPC1 with myosin VI and recruitment of overexpressed myosin VI to membrane structures, but not for the association of GIPC1 with such structures; 3) GIPC1/myosin VI complexes coordinately move within cellular extensions of the cell in an actin-dependent and microtubule-independent manner; and 4) blocking either GIPC1 interactions with myosin VI or GLUT1 interactions with GIPC1 disrupts normal GLUT1 trafficking in polarized epithelial cells, leading to a reduction in the level of GLUT1 in the plasma membrane and concomitant accumulation in internal membrane structures.
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Affiliation(s)
- Brent C Reed
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, LA 71130, USA.
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80
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Hoepfner S, Severin F, Cabezas A, Habermann B, Runge A, Gillooly D, Stenmark H, Zerial M. Modulation of Receptor Recycling and Degradation by the Endosomal Kinesin KIF16B. Cell 2005; 121:437-50. [PMID: 15882625 DOI: 10.1016/j.cell.2005.02.017] [Citation(s) in RCA: 299] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2004] [Revised: 09/27/2004] [Accepted: 02/16/2005] [Indexed: 12/31/2022]
Abstract
Different classes of endosomes exhibit a characteristic intracellular steady-state distribution governed by interactions with the cytoskeleton. We found a kinesin-3, KIF16B, that transports early endosomes to the plus end of microtubules in a process regulated by the small GTPase Rab5 and its effector, the phosphatidylinositol-3-OH kinase hVPS34. In vivo, KIF16B overexpression relocated early endosomes to the cell periphery and inhibited transport to the degradative pathway. Conversely, expression of dominant-negative mutants or ablation of KIF16B by RNAi caused the clustering of early endosomes to the perinuclear region, delayed receptor recycling to the plasma membrane, and accelerated degradation. These results suggest that KIF16B, by regulating the plus end motility of early endosomes, modulates the intracellular localization of early endosomes and the balance between receptor recycling and degradation. We propose that this mechanism could have important implications for signaling.
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Affiliation(s)
- Sebastian Hoepfner
- Max-Planck Institute for Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany
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81
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Dance AL, Miller M, Seragaki S, Aryal P, White B, Aschenbrenner L, Hasson T. Regulation of myosin-VI targeting to endocytic compartments. Traffic 2005; 5:798-813. [PMID: 15355515 DOI: 10.1111/j.1600-0854.2004.00224.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Myosin-VI has been implicated in endocytic trafficking at both the clathrin-coated and uncoated vesicle stages. The identification of alternative splice forms led to the suggestion that splicing defines the vesicle type to which myosin-VI is recruited. In contrast to this hypothesis, we find that in all cell types examined, myosin-VI is associated with uncoated endocytic vesicles, regardless of splice form. GIPC, a PDZ-domain containing adapter protein, co-assembles with myosin-VI on these vesicles. Myosin-VI is only recruited to clathrin-coated vesicles in cells that express high levels of Dab2, a clathrin-binding adapter protein. Overexpression of Dab2 is sufficient to reroute myosin-VI to clathrin-coated pits in cells where myosin-VI is normally associated with uncoated vesicles. In normal rat kidney (NRK) cells, which express high endogenous levels of Dab2, splicing of the globular tail domain further modulates targeting of ectopically expressed myosin-VI. Although myosin-VI can be recruited to clathrin-coated pits, we find no requirement for myosin-VI motor activity in endocytosis in NRK cells. Instead, our data suggest that myosin-VI recruitment to clathrin-coated pits may be an early step in the recruitment of GIPC to the vesicle surface.
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Affiliation(s)
- Amber L Dance
- Section of Cell and Developmental Biology, Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093, USA
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82
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Hosein RE, Williams SA, Gavin RH. Directed motility of phagosomes inTetrahymena thermophila requires actin and Myo1p, a novel unconventional myosin. ACTA ACUST UNITED AC 2005; 61:49-60. [PMID: 15810016 DOI: 10.1002/cm.20065] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The phagosome cycle was investigated in Tetrahymena thermophila, which had internalized fluorescent latex beads. Confocal microscopy of cells from a GFP-actin strain revealed actin filaments that extended 3-5 mum from the periphery of fluorescent phagosomes. In GFP-actin cells and in wild-type cells, motility of fluorescent phagosomes was directed from the oral cavity to the posterior end of the cell. Although 60% of fluorescent phagosomes in the MYO1-knockout strain were motile, movement of phagosomes was not directed toward the posterior end of the cell and was random. Forty percent of fluorescent phagosomes in knockout cells were non-motile in contrast to only 20% non-motile phagosomes in wild-type cells. The increased incidence of non-motile phagosomes in the knockout strain could reflect absence of Myo1p as a motor. Another myosin or other molecular motors could power random movement of phagosomes in the MYO1-knockout strain. In latrunculin-treated GFP-actin cells, movement of fluorescent phagosomes was random. Average velocity of random movement of fluorescent phagosomes in the knockout strain and in latrunculin-treated cells was statistically the same as the average velocity (2.0 +/- 1.9 microm/min) of phagosomes in GFP-actin cells. These findings are an indication that dynamic actin and Myo1p are required for directed motility of phagosomes.
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Affiliation(s)
- Roland E Hosein
- Department of Biology, Brooklyn College of the City University of New York, Brooklyn, New York 11210, USA
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83
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Seiler C, Ben-David O, Sidi S, Hendrich O, Rusch A, Burnside B, Avraham KB, Nicolson T. Myosin VI is required for structural integrity of the apical surface of sensory hair cells in zebrafish. Dev Biol 2004; 272:328-38. [PMID: 15282151 DOI: 10.1016/j.ydbio.2004.05.004] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2004] [Revised: 04/30/2004] [Accepted: 05/04/2004] [Indexed: 10/26/2022]
Abstract
Unconventional myosins have been associated with hearing loss in humans, mice, and zebrafish. Mutations in myosin VI cause both recessive and dominant forms of nonsyndromic deafness in humans and deafness in Snell's waltzer mice associated with abnormal fusion of hair cell stereocilia. Although myosin VI has been implicated in diverse cellular processes such as vesicle trafficking and epithelial morphogenesis, the role of this protein in the sensory hair cells remains unclear. To investigate the function of myosin VI in zebrafish, we cloned and examined the expression pattern of myosin VI, which is duplicated in the zebrafish genome. One duplicate, myo6a, is expressed in a ubiquitous pattern during early development and at later stages, and is highly expressed in the brain, gut, and kidney. myo6b, on the other hand, is predominantly expressed in the sensory epithelium of the ear and lateral line at all developmental stages examined. Both molecules have different splice variants expressed in these tissues. Using a candidate gene approach, we show that myo6b is satellite, a gene responsible for auditory/vestibular defects in zebrafish larvae. Examination of hair cells in satellite mutants revealed that stereociliary bundles are irregular and disorganized. At the ultrastructural level, we observed that the apical surface of satellite mutant hair cells abnormally protrudes above the epithelium and the membrane near the base of the stereocilia is raised. At later stages, stereocilia fused together. We conclude that zebrafish myo6b is required for maintaining the integrity of the apical surface of hair cells, suggesting a conserved role for myosin VI in regulation of actin-based interactions with the plasma membrane.
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Affiliation(s)
- Christoph Seiler
- Max-Planck-Institut fur Entwicklungsbiologie, 72076 Tubingen, Germany
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84
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Chen G, Raman P, Bhonagiri P, Strawbridge AB, Pattar GR, Elmendorf JS. Protective effect of phosphatidylinositol 4,5-bisphosphate against cortical filamentous actin loss and insulin resistance induced by sustained exposure of 3T3-L1 adipocytes to insulin. J Biol Chem 2004; 279:39705-9. [PMID: 15277534 PMCID: PMC2413414 DOI: 10.1074/jbc.c400171200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Muscle and fat cells develop insulin resistance when cultured under hyperinsulinemic conditions for sustained periods. Recent data indicate that early insulin signaling defects do not fully account for the loss of insulin action. Given that cortical filamentous actin (F-actin) represents an essential aspect of insulin regulated glucose transport, we tested to see whether cortical F-actin structure was compromised during chronic insulin treatment. The acute effect of insulin on GLUT4 translocation and glucose uptake was diminished in 3T3-L1 adipocytes exposed to a physiological level of insulin (5 nm) for 12 h. This insulin-induced loss of insulin responsiveness was apparent under both low (5.5 mm) and high (25 mm) glucose concentrations. Microscopic and biochemical analyses revealed that the hyperinsulinemic state caused a marked loss of cortical F-actin. Since recent data link phosphatidylinositol 4,5-bisphosphate (PIP(2)) to actin cytoskeletal mechanics, we tested to see whether the insulin-resistant condition affected PIP(2) and found a noticeable loss of this lipid from the plasma membrane. Using a PIP(2) delivery system, we replenished plasma membrane PIP(2) in cells following the sustained insulin treatment and observed a restoration in cortical F-actin and insulin responsiveness. These data reveal a novel molecular aspect of insulin-induced insulin resistance involving defects in PIP(2)/actin regulation.
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Affiliation(s)
- Guoli Chen
- Departments of Cellular & Integrative Physiology, Indiana University School of Medicine, Center for Diabetes Research, Indianapolis, Indiana 46202
| | - Priya Raman
- Departments of Cellular & Integrative Physiology, Indiana University School of Medicine, Center for Diabetes Research, Indianapolis, Indiana 46202
| | - Padma Bhonagiri
- Departments of Cellular & Integrative Physiology, Indiana University School of Medicine, Center for Diabetes Research, Indianapolis, Indiana 46202
| | - Andrew B. Strawbridge
- Departments of Cellular & Integrative Physiology, Indiana University School of Medicine, Center for Diabetes Research, Indianapolis, Indiana 46202
| | - Guruprasad R. Pattar
- Departments of Cellular & Integrative Physiology, Indiana University School of Medicine, Center for Diabetes Research, Indianapolis, Indiana 46202
| | - Jeffrey S. Elmendorf
- Departments of Cellular & Integrative Physiology, Indiana University School of Medicine, Center for Diabetes Research, Indianapolis, Indiana 46202
- Biochemistry & Molecular Biology, Indiana University School of Medicine, Center for Diabetes Research, Indianapolis, Indiana 46202
- ** To whom correspondence should be addressed: Dept. of Cellular & Integrative Physiology, Indiana University School of Medicine, Center for Diabetes Research, Indianapolis, IN 46202. Tel.: 317-274-7852; Fax: 317-274-3318; E-mail:
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85
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Swiatecka-Urban A, Boyd C, Coutermarsh B, Karlson KH, Barnaby R, Aschenbrenner L, Langford GM, Hasson T, Stanton BA. Myosin VI regulates endocytosis of the cystic fibrosis transmembrane conductance regulator. J Biol Chem 2004; 279:38025-31. [PMID: 15247260 DOI: 10.1074/jbc.m403141200] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic AMP-regulated Cl(-) channel expressed in the apical plasma membrane in fluid-transporting epithelia. Although CFTR is rapidly endocytosed from the apical membrane of polarized epithelial cells and efficiently recycled back to the plasma membrane, little is known about the molecular mechanisms regulating CFTR endocytosis and endocytic recycling. Myosin VI, an actin-dependent, minus-end directed mechanoenzyme, has been implicated in clathrin-mediated endocytosis in epithelial cells. The goal of this study was to determine whether myosin VI regulates CFTR endocytosis. Endogenous, apical membrane CFTR in polarized human airway epithelial cells (Calu-3) formed a complex with myosin VI, the myosin VI adaptor protein Disabled 2 (Dab2), and clathrin. The tail domain of myosin VI, a dominant-negative recombinant fragment, displaced endogenous myosin VI from interacting with Dab2 and CFTR and increased the expression of CFTR in the plasma membrane by reducing CFTR endocytosis. However, the myosin VI tail fragment had no effect on the recycling of endocytosed CFTR or on fluid-phase endocytosis. CFTR endocytosis was decreased by cytochalasin D, an actin-filament depolymerizing agent. Taken together, these data indicate that myosin VI and Dab2 facilitate CFTR endocytosis by a mechanism that requires actin filaments.
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