Myosin-X Induces Filopodia by Multiple Elongation Mechanism

Abstract

Filopodia are actin-rich finger-like cytoplasmic projections extending from the leading edge of cells. Unconventional myosin-X is involved in the protrusion of filopodia. However, the underlying mechanism of myosin-X-induced filopodia formation is obscure. Here, we studied the movements of myosin-X during filopodia protrusion using a total internal reflection microscope to clarify the mechanism of myosin-X-induced filopodia formation. Myosin-X was recruited to the discrete site at the leading edge where it assembles with exponential kinetics before the filopodia extension. The myosin-X-induced filopodia showed repeated extension-retraction cycles with each extension of 2.4 μm, which was critical to produce long filopodia. Myosin-X, lacking the FERM domain, could move to the tip as does the wild type. However, it was transported toward the cell body during filopodia retraction, did not undergo multiple extension-retraction cycles, and failed to produce long filopodia. During the filopodia protrusion, the single molecules of full-length myosin-X moved within filopodia. The majority of the fluorescence spots showed two-step photobleaching, suggesting that the moving myosin-X is a dimer. Deletion of the FERM domain did not change the movement at the single molecule level with the same velocity of ∼600 nm/s as wild-type, suggesting that the myosin-X in filopodia moves without interaction with the attached membrane via the FERM domain. Based upon these results, we have proposed a model of myosin-X-induced filopodia protrusion. Filopodia are actin-rich finger-like cytoplasmic projections extending from the leading edge of cells. Unconventional myosin-X is involved in the protrusion of filopodia. However, the underlying mechanism of myosin-X-induced filopodia formation is obscure. Here, we studied the movements of myosin-X during filopodia protrusion using a total internal reflection microscope to clarify the mechanism of myosin-X-induced filopodia formation. Myosin-X was recruited to the discrete site at the leading edge where it assembles with exponential kinetics before the filopodia extension. The myosin-X-induced filopodia showed repeated extension-retraction cycles with each extension of 2.4 μm, which was critical to produce long filopodia. Myosin-X, lacking the FERM domain, could move to the tip as does the wild type. However, it was transported toward the cell body during filopodia retraction, did not undergo multiple extension-retraction cycles, and failed to produce long filopodia. During the filopodia protrusion, the single molecules of full-length myosin-X moved within filopodia. The majority of the fluorescence spots showed two-step photobleaching, suggesting that the moving myosin-X is a dimer. Deletion of the FERM domain did not change the movement at the single molecule level with the same velocity of ∼600 nm/s as wild-type, suggesting that the myosin-X in filopodia moves without interaction with the attached membrane via the FERM domain. Based upon these results, we have proposed a model of myosin-X-induced filopodia protrusion. IntroductionCells change their shape during the diverse motile processes, and the cytoskeletal structural reorganization is a fundamental element in cellular motility and contractile processes. There are two types of actin cytoskeletal architectures, filopodia and lamellipodia, both playing an important role in such motile events. Filopodia are slender projections, which extend from the leading edge of migrating cells and play an important role in a wide range of cell motilities such as cancer cell migration (1Bennett R.D. Mauer A.S. Strehler E.E. J. Biol. Chem. 2007; 282: 3205-3212Abstract Full Text Full Text PDF PubMed Scopus (38) Google Scholar, 2Wicki A. Lehembre F. Wick N. Hantusch B. Kerjaschki D. Christofori G. Cancer Cell. 2006; 9: 261-272Abstract Full Text Full Text PDF PubMed Scopus (453) Google Scholar) and neuronal path finding (3Bentley D. O'Connor T.P. Curr. Opin. Neurobiol. 1994; 4: 43-48Crossref PubMed Scopus (168) Google Scholar, 4Lewis A.K. Bridgman P.C. J. Cell Biol. 1992; 119: 1219-1243Crossref PubMed Scopus (261) Google Scholar). Although many studies have examined the role of actin and actin-binding proteins in the dynamics of membrane protrusion (5Biyasheva A. Svitkina T. Kunda P. Baum B. Borisy G. J. Cell Sci. 2004; 117: 837-848Crossref PubMed Scopus (94) Google Scholar, 6Nakagawa H. Miki H. Nozumi M. Takenawa T. Miyamoto S. Wehland J. Small J.V. J. Cell Sci. 2003; 116: 2577-2583Crossref PubMed Scopus (108) Google Scholar, 7Lebrand C. Dent E.W. Strasser G.A. Lanier L.M. Krause M. Svitkina T.M. Borisy G.G. Gertler F.B. Neuron. 2004; 42: 37-49Abstract Full Text Full Text PDF PubMed Scopus (250) Google Scholar), recent attention has been given to myosin-X, a vertebrate-specific unconventional myosin, and its role in the production of filopodia (8Tokuo H. Ikebe M. Biochem. Biophys. Res. Commun. 2004; 319: 214-220Crossref PubMed Scopus (125) Google Scholar, 9Sousa A.D. Cheney R.E. Trends Cell Biol. Full Text Full Text PDF PubMed Scopus Google Scholar, Cheney R.E. Sci. 2006; PubMed Scopus Google Scholar, H. P. A.D. A. Cheney R.E. S. Cell Biol. 2004; PubMed Scopus Google Scholar, Cheney R.E. J. Cell Sci. PubMed Google Scholar, M. M. H. G.A. N. P. A. F. S. S. Trends Biochem. Sci. Full Text Full Text PDF PubMed Scopus Google Scholar). has been that myosin-X at the of filopodia (8Tokuo H. Ikebe M. Biochem. Biophys. Res. Commun. 2004; 319: 214-220Crossref PubMed Scopus (125) Google Scholar, Cheney R.E. Sci. 2006; PubMed Scopus Google Scholar, Cheney R.E. J. Cell Sci. PubMed Google Scholar), and myosin-X has been to filopodia protrusion (8Tokuo H. Ikebe M. Biochem. Biophys. Res. Commun. 2004; 319: 214-220Crossref PubMed Scopus (125) Google Scholar, H. P. A.D. A. Cheney R.E. S. Cell Biol. 2004; PubMed Scopus Google Scholar, Cheney R.E. Cell Biol. 4: PubMed Scopus (261) Google Scholar). have the that myosin-X a critical role in the production of is of an domain that and to a of that a domain, which the a and a domain at the Cheney R.E. Cell Biol. 4: PubMed Scopus (261) Google Scholar, F. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The domain of in a domain, which with and a internal reflection domain, which have a role myosin-X to the membrane via H. P. A.D. A. Cheney R.E. S. Cell Biol. 2004; PubMed Scopus Google Scholar, Cheney R.E. J. Cell Sci. PubMed Google Scholar, M. M. H. G.A. N. P. A. F. S. S. Trends Biochem. Sci. Full Text Full Text PDF PubMed Scopus Google was that the role of myosin-X in filopodia formation is the of the molecules to which actin However, we that the myosin-X without the domain, the FERM domain, filopodia upon suggesting that the formation of myosin-X is critical the of filopodia H. Ikebe M. J. Cell Biol. 2007; PubMed Scopus Google Scholar). the filopodia myosin-X lacking the domain and the filopodia full-length myosin-X Cheney R.E. Sci. 2006; PubMed Scopus Google Scholar, H. P. A.D. A. Cheney R.E. S. Cell Biol. 2004; PubMed Scopus Google Scholar). finding that the domain of myosin-X is long and filopodia. is to the of the molecules that are the production of long and filopodia. the underlying mechanism and the role of the domain are have been to the of myosin-X Ikebe M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, M. F. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, S. Sci. PubMed Scopus Google Scholar). was that myosin-X is a that is a movement Ikebe M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). the that myosin-X is a it move in the cell with the membrane M. F. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). was that myosin-X moves actin not single actin with a velocity of ∼600 nm/s S. Sci. PubMed Scopus Google Scholar). was that myosin-X its in cells in the where actin such as filopodia. it was that the movement of single myosin-X molecules toward the in cells T. A.D. Cheney R.E. Curr. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). the using the microscope the the in of the molecules and their the movement of myosin-X in filopodia is not is critical to the movements of myosin-X during of filopodia protrusion and to the mechanism underlying myosin-X-induced filopodia the we the movement of myosin-X with in filopodia of cells using a total internal reflection microscope T. Cell Biol. 2003; 4: Google Scholar). to the filopodia attached to a in cells. the T. A.D. Cheney R.E. Curr. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar) the myosin-X we the role of FERM domain the movements of myosin-X at the Based upon the of of myosin-X and of FERM domain we a model of the myosin-X-induced the role of the domain the movement and of myosin-X in filopodia extension in we two myosin-X a full-length and a FERM and that the of a of in which myosin-X at the and The filopodia was that the of filopodia was not the FERM domain is with a H. P. A.D. A. Cheney R.E. S. Cell Biol. 2004; PubMed Scopus Google Scholar). 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G. Sci. 2004; PubMed Scopus Google Scholar). The the tip and the site was as a of and it was that the extension velocity was before the and the velocity with the and during the extension and during the the and The was with single with the of nm/s and of nm/s that was not with single with a nm/s and nm/s the of of to of it is that the FERM domain the of nm/s during filopodia extension. that these with the movement of the using a Cell 1992; PubMed Scopus Google Scholar, A. T. J. Cell Biol. PubMed Scopus Google Scholar). the FERM domain with the membrane via H. P. A.D. A. Cheney R.E. S. 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P. A.D. A. Cheney R.E. S. Cell Biol. 2004; PubMed Scopus Google Scholar). we that the FERM domain of myosin-X is important to the of extension The of the FERM domain in the of myosin-X during the The in to the movement from the actin However, was at the suggesting that the FERM domain a role in myosin-X at the was that the FERM domain of myosin-X with H. P. A.D. A. Cheney R.E. S. Cell Biol. 2004; PubMed Scopus Google Scholar). that at the tip via interaction with the membrane the FERM and that is the of filopodia in of filopodia velocity from the in from the in velocity from the in from the in of the from the in from the in velocity of the of the extension during each of of extension of movements from the in in a Although the of the FERM domain the extension the the and the extension was FERM that the extension before and in the of model and A. B. Biophys. J. Full Text Full Text PDF PubMed Scopus Google Scholar) the of the of filopodia extension to μm, which with and that the of the membrane is the extension and the the extension. is that the of filopodia to the at the is the finding is the in the filopodia extension the cells and Although was in the and the of the FERM domain the extension velocity of filopodia and The of filopodia was to of myosin-X the actin to the membrane via FERM is that myosin-X a role in both the and the of showed that myosin-X moved actin with velocity within which is with that of in that myosin-X moved actin in filopodia at a level S. Sci. PubMed Scopus Google Scholar). The was to the velocity in of the of myosin-X with J. Ikebe Ikebe M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). that the full-length myosin-X is the in filopodia and is to a myosin-X in is a Cheney R.E. Cell Biol. 4: PubMed Scopus (261) Google the we to the myosin-X motilities the membrane at the leading the not the finding that myosin-X move where actin S. Sci. PubMed Scopus Google Scholar). myosin-X is in cells before the cell and a at the of filopodia H. Ikebe M. J. Cell Biol. 2007; PubMed Scopus Google Scholar). that myosin-X at the leading edge with exponential kinetics to produce the of filopodia. myosin-X to the actin S. Sci. PubMed Scopus Google Scholar), each myosin-X to two actin within the actin that myosin-X the of actin which myosin-X at the site of filopodia. is of the movement of myosin-X the membrane H. Ikebe M. J. Cell Biol. 2007; PubMed Scopus Google Scholar). The of the actin is the of the filopodia protrusion, and at actin are to the membrane filopodia extension as A. B. Biophys. J. Full Text Full Text PDF PubMed Scopus Google Scholar). that the of the actin myosin-X the of the actin a and the filopodia extension the of of actin the membrane from the extension we that the of the domain of myosin-X, not the FERM domain, are important the of filopodia formation Cheney R.E. Sci. 2006; PubMed Scopus Google Scholar, Cheney R.E. Cell Biol. 4: PubMed Scopus (261) Google Scholar, H. Ikebe M. J. Cell Biol. 2007; PubMed Scopus Google the we the model the mechanism of myosin-X-induced filopodia protrusion the filopodia the myosin-X molecules are recruited to the discrete at the where a the with their a of filopodia. The in the of myosin-X and its molecules the of of the the exponential in myosin-X The myosin-X moves toward the of the actin toward the tip of the filopodia without to the the actin to actin the membrane P. G. S. Biol. Cell. PubMed Scopus Google Scholar, P. G. Sci. 2004; PubMed Scopus Google Scholar). the actin and the cell is actin move toward the cell body a R.D. Biophys. PubMed Scopus Google Scholar, D. C. PubMed Scopus Google Scholar, C. J. Biol. Cell. PubMed Scopus Google Scholar). During the cell the membrane to the myosin-X at the tip to the membrane via FERM the the membrane the tip and Myosin-X molecules at the tip to the actin a of the myosin-X moves with myosin-X moves toward the the filopodia not multiple cycles, the interaction of myosin-X and the is the that the myosin-X the tip the actin and the myosin-X a the actin the of the FERM domain, the of actin in myosin-X in the filopodia without at the myosin-X to membrane model myosin-X-induced extension. The model is in the Myosin-X moves to the tip with The is at the During actin myosin-X at the tip as a of to Filopodia to the of the tip from the Myosin-X to actin and that the membrane to produce actin to extend and myosin-X moves toward the the movement of myosin-X during filopodia protrusion was using a microscope in cells to clarify the mechanism of filopodia that the formation of myosin-X with is important the of filopodia H. Ikebe M. J. Cell Biol. 2007; PubMed Scopus Google Scholar). that the and of the two critical the of filopodia. However, it is myosin-X filopodia formation and the extension. is that myosin-X has a to the the cytoskeletal structural change and membrane extension. The the of the of filopodia extension. IntroductionCells change their shape during the diverse motile processes, and the cytoskeletal structural reorganization is a fundamental element in cellular motility and contractile processes. There are two types of actin cytoskeletal architectures, filopodia and lamellipodia, both playing an important role in such motile events. Filopodia are slender projections, which extend from the leading edge of migrating cells and play an important role in a wide range of cell motilities such as cancer cell migration (1Bennett R.D. Mauer A.S. Strehler E.E. J. Biol. Chem. 2007; 282: 3205-3212Abstract Full Text Full Text PDF PubMed Scopus (38) Google Scholar, 2Wicki A. Lehembre F. Wick N. Hantusch B. Kerjaschki D. Christofori G. Cancer Cell. 2006; 9: 261-272Abstract Full Text Full Text PDF PubMed Scopus (453) Google Scholar) and neuronal path finding (3Bentley D. O'Connor T.P. Curr. Opin. Neurobiol. 1994; 4: 43-48Crossref PubMed Scopus (168) Google Scholar, 4Lewis A.K. Bridgman P.C. J. Cell Biol. 1992; 119: 1219-1243Crossref PubMed Scopus (261) Google Scholar). Although many studies have examined the role of actin and actin-binding proteins in the dynamics of membrane protrusion (5Biyasheva A. Svitkina T. Kunda P. Baum B. Borisy G. J. Cell Sci. 2004; 117: 837-848Crossref PubMed Scopus (94) Google Scholar, 6Nakagawa H. Miki H. Nozumi M. Takenawa T. Miyamoto S. Wehland J. Small J.V. J. Cell Sci. 2003; 116: 2577-2583Crossref PubMed Scopus (108) Google Scholar, 7Lebrand C. Dent E.W. Strasser G.A. Lanier L.M. Krause M. Svitkina T.M. Borisy G.G. Gertler F.B. Neuron. 2004; 42: 37-49Abstract Full Text Full Text PDF PubMed Scopus (250) Google Scholar), recent attention has been given to myosin-X, a vertebrate-specific unconventional myosin, and its role in the production of filopodia (8Tokuo H. Ikebe M. Biochem. Biophys. Res. Commun. 2004; 319: 214-220Crossref PubMed Scopus (125) Google Scholar, 9Sousa A.D. Cheney R.E. Trends Cell Biol. Full Text Full Text PDF PubMed Scopus Google Scholar, Cheney R.E. Sci. 2006; PubMed Scopus Google Scholar, H. P. A.D. A. Cheney R.E. S. Cell Biol. 2004; PubMed Scopus Google Scholar, Cheney R.E. J. Cell Sci. PubMed Google Scholar, M. M. H. G.A. N. P. A. F. S. S. Trends Biochem. Sci. Full Text Full Text PDF PubMed Scopus Google Scholar). has been that myosin-X at the of filopodia (8Tokuo H. Ikebe M. Biochem. Biophys. Res. Commun. 2004; 319: 214-220Crossref PubMed Scopus (125) Google Scholar, Cheney R.E. Sci. 2006; PubMed Scopus Google Scholar, Cheney R.E. J. Cell Sci. PubMed Google Scholar), and myosin-X has been to filopodia protrusion (8Tokuo H. Ikebe M. Biochem. Biophys. Res. Commun. 2004; 319: 214-220Crossref PubMed Scopus (125) Google Scholar, H. P. A.D. A. Cheney R.E. S. Cell Biol. 2004; PubMed Scopus Google Scholar, Cheney R.E. Cell Biol. 4: PubMed Scopus (261) Google Scholar). have the that myosin-X a critical role in the production of is of an domain that and to a of that a domain, which the a and a domain at the Cheney R.E. Cell Biol. 4: PubMed Scopus (261) Google Scholar, F. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The domain of in a domain, which with and a internal reflection domain, which have a role myosin-X to the membrane via H. P. A.D. A. Cheney R.E. S. Cell Biol. 2004; PubMed Scopus Google Scholar, Cheney R.E. J. Cell Sci. PubMed Google Scholar, M. M. H. G.A. N. P. A. F. S. S. Trends Biochem. Sci. Full Text Full Text PDF PubMed Scopus Google was that the role of myosin-X in filopodia formation is the of the molecules to which actin However, we that the myosin-X without the domain, the FERM domain, filopodia upon suggesting that the formation of myosin-X is critical the of filopodia H. Ikebe M. J. Cell Biol. 2007; PubMed Scopus Google Scholar). the filopodia myosin-X lacking the domain and the filopodia full-length myosin-X Cheney R.E. Sci. 2006; PubMed Scopus Google Scholar, H. P. A.D. A. Cheney R.E. S. Cell Biol. 2004; PubMed Scopus Google Scholar). finding that the domain of myosin-X is long and filopodia. is to the of the molecules that are the production of long and filopodia. the underlying mechanism and the role of the domain are have been to the of myosin-X Ikebe M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, M. F. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, S. Sci. PubMed Scopus Google Scholar). was that myosin-X is a that is a movement Ikebe M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). the that myosin-X is a it move in the cell with the membrane M. F. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). was that myosin-X moves actin not single actin with a velocity of ∼600 nm/s S. Sci. PubMed Scopus Google Scholar). was that myosin-X its in cells in the where actin such as filopodia. it was that the movement of single myosin-X molecules toward the in cells T. A.D. Cheney R.E. Curr. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). the using the microscope the the in of the molecules and their the movement of myosin-X in filopodia is not is critical to the movements of myosin-X during of filopodia protrusion and to the mechanism underlying myosin-X-induced filopodia the we the movement of myosin-X with in filopodia of cells using a total internal reflection microscope T. Cell Biol. 2003; 4: Google Scholar). to the filopodia attached to a in cells. the T. A.D. Cheney R.E. Curr. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar) the myosin-X we the role of FERM domain the movements of myosin-X at the Based upon the of of myosin-X and of FERM domain we a model of the myosin-X-induced