Mouse MIM binds ATP-G-actin with higher affinity (KD = 0.06 μm) than ADP-G-actin (KD = 0.3 μm) via its C-terminal WH2 domain, inhibiting actin filament nucleation in vitro.
MIM is an ATP-G-actin binding protein that regulates cytoskeletal dynamics in specialized mammalian cell-types, including developing cardiac muscles.
The WH2 (WASP homology domain-2) is a small actin monomer-binding motif and is found in many proteins that regulate the actin cytoskeleton, including the β-thymosins, ciboulot, WASP, and verprolin/WIP (WASP-interacting protein). In sequence database searches we identified a novel mouse protein containing a WH2 domain in its C-terminal region. This mouse gene also shows strong sequence homology to human MIM (Missing in Metastasis), a cDNA fragment that is present in non-metastatic but absent in metastatic bladder cancer cell lines. Northern blot and in situ hybridizations show that MIM is strongly expressed in the developing neurons and skeletal and cardiac muscles in mouse embryos. In adult mice, the strongest expression of MIM mRNA is in liver, outer layers of the kidney, and in the Purkinje cells of the brain. Recombinant MIM protein interacts with actin monomers and inhibits actin filament nucleation in vitro. However, the MIM/ATP-G-actin complex can participate in actin filament assembly at the barbed end. MIM binds ATP-G-actin with a higher affinity (K D = 0.06 μm) than ADP-G-actin (K D = 0.3 μm) and inhibits the nucleotide exchange on actin monomers. Site-directed mutagenesis demonstrates that the actin monomer-binding site resides in the C-terminal WH2 domain of MIM. Overexpression of mouse MIM in NIH 3T3 cells results in the disappearance of actin stress fibers and appearance of abnormal actin filament structures. These data show that MIM is an ATP-G-actin binding protein that regulates cytoskeletal dynamics in specialized mammalian cell-types. The WH2 (WASP homology domain-2) is a small actin monomer-binding motif and is found in many proteins that regulate the actin cytoskeleton, including the β-thymosins, ciboulot, WASP, and verprolin/WIP (WASP-interacting protein). In sequence database searches we identified a novel mouse protein containing a WH2 domain in its C-terminal region. This mouse gene also shows strong sequence homology to human MIM (Missing in Metastasis), a cDNA fragment that is present in non-metastatic but absent in metastatic bladder cancer cell lines. Northern blot and in situ hybridizations show that MIM is strongly expressed in the developing neurons and skeletal and cardiac muscles in mouse embryos. In adult mice, the strongest expression of MIM mRNA is in liver, outer layers of the kidney, and in the Purkinje cells of the brain. Recombinant MIM protein interacts with actin monomers and inhibits actin filament nucleation in vitro. However, the MIM/ATP-G-actin complex can participate in actin filament assembly at the barbed end. MIM binds ATP-G-actin with a higher affinity (K D = 0.06 μm) than ADP-G-actin (K D = 0.3 μm) and inhibits the nucleotide exchange on actin monomers. Site-directed mutagenesis demonstrates that the actin monomer-binding site resides in the C-terminal WH2 domain of MIM. Overexpression of mouse MIM in NIH 3T3 cells results in the disappearance of actin stress fibers and appearance of abnormal actin filament structures. These data show that MIM is an ATP-G-actin binding protein that regulates cytoskeletal dynamics in specialized mammalian cell-types. WASP homology domain-2 Wiscott-Aldrich syndrome protein WASP-interacting protein cyclase-associated protein expressed sequence tag green fluorescent protein glutathione-S-transferase missing in metastasis protein C-terminal half of MIM protein 7-chloro-4-nitrobenz-2-oxa-1,3-diazole dithiothreitol The actin cytoskeleton is central in a number of cellular processes such as motility, morphogenesis, cytokinesis, and endocytosis. The structure and dynamics of the actin cytoskeleton are spatially and temporally regulated by a large number of actin-binding proteins, whose own activities and localities are precisely regulated by various signaling pathways (1Pollard T.D. Blanchoin L. Mullins R.D. Annu. Rev. Biophys. Biomolec. Struct. 2000; 29: 545-576Google Scholar, 2Gimona M. Djinovic-Carugo K. Kranewitter W.J. Winder S.J. FEBS Lett. 2002; 513: 98-106Google Scholar, 3Van Troys M. Vandekerckhove J. Ampe C. Biochim. Biophys. Acta. 1999; 1448: 323-348Google Scholar, 4Lappalainen P. Kessels M.M. Cope J.T.V. Drubin D.G. Mol. Biol. Cell. 1998; 9: 1951-1959Google Scholar). Sequence and structural data on actin-binding proteins has revealed that many of these proteins interact with actin through a relatively small number of protein motifs. These include the calponin homology domain, the gelsolin homology domain, the actin-depolymerizing-factor homology domain, and the WASP homology 2 (WH2)1domain (for reviews see 2–5).The WH2 domain is a small (∼35 residue) protein motif that interacts only with monomeric actin (5Paunola E. Mattila P.K. Lappalainen P. FEBS Lett. 2002; 513: 92-97Google Scholar, 6Symons M. Derry J.M. Karlak B.J. Jiang S. Lemahieu V. McCormick F. Francke U. Abo A. Cell. 1996; 84: 723-734Google Scholar). WH2 domains are found in many regulators of actin dynamics, including β-thymosins and ciboulot, which bind actin monomers and regulate filament assembly. β-thymosins are actin monomer-sequestering proteins, whereas ciboulot promotes actin assembly at the barbed end of the filaments (7Pantaloni D. Carlier M.-F. Cell. 1993; 75: 1007-1014Google Scholar, 8Boquet I. Boujemaa R. Carlier M.F. Preat T. Cell. 2000; 102: 797-808Google Scholar). WH2 domains are also present in more complex proteins such as WASP/Scar, verprolin/WIP, and Srv2/CAP. These are multifunctional regulators of actin dynamics that link intracellular signaling pathways to actin dynamics (5Paunola E. Mattila P.K. Lappalainen P. FEBS Lett. 2002; 513: 92-97Google Scholar). For example, WASP and Scar mediate signals from PIP2 and the small GTPases Cdc42 and Rac to the actin cytoskeleton by inducing actin assembly through activation of the Arp2/3 complex (9Machesky L.M. Insall R.H. Curr. Biol. 1998; 8: 1347-1356Google Scholar, 10Higgs H.N. Pollard T.D. J. Cell Biol. 2000; 150: 1311-1320Google Scholar, 11Prehoda K.E. Scott J.A. Mullins R.D. Lim W.A. Science. 2000; 290: 801-806Google Scholar). The WH2 domain is essential for the activity of WASP and Scar and is believed to facilitate the assembly of actin monomers to the newly formed filament ends (12Yarar D. D'Alessio J.A. Jeng R.L. Welch M.D. Mol. Biol. Cell. 2002; 13: 4045-4059Google Scholar, 13Welch M.D. Mullins R.D. Annu. Rev. Cell Dev. Biol. 2002; 18: 247-288Google Scholar). Also verprolin/WIP proteins interact with actin monomers through their WH2 domains, but the biological role of their actin monomer-binding activity is still unclear (14Thanabalu T. Munn A.L. EMBO J. 2001; 20: 6979-6989Google Scholar).We searched sequence databases for WH2 domain-containing proteins in mammals, Drosophila melanogaster,Caenorhabditis elegans, andSaccharomyces cerevisiae. In addition to the previously characterized WH2 domain proteins (β-thymosins, ciboulot, WASP, verprolin/WIP, Scar, Srv2/CAP) we identified several previously unknown WH2 domain-containing proteins (5Paunola E. Mattila P.K. Lappalainen P. FEBS Lett. 2002; 513: 92-97Google Scholar). One of these proteins is particularly interesting because it is highly homologous to a human cDNA fragment named MIM (Missing In Metastasis) that was recently identified in a differential screen for mRNAs specifically expressed in non-metastatic bladder cancer cells (15Lee Y.-G. Macoska J.A. Korenchuk S. Pienta K.J. Neoplasia. 2002; 4: 291-294Google Scholar).We show that mouse MIM is an actin monomer-binding protein that efficiently inhibits the nucleotide exchange on actin monomers and actin filament nucleation in vitro. The strong actin-modulating activities reside in the C-terminal WH2 domain of MIM. We found that MIM is strongly expressed in the developing heart, skeletal muscle, and central nervous system. In adult mouse tissues, strong expression levels are detected in liver and in certain regions of brain and kidney. Overexpression of MIM results in the disappearance of stress fibers and formation of abnormal F-actin structures in NIH 3T3 cells, suggesting that MIM regulates the dynamics of the actin monomer pool in specialized mammalian cells.DISCUSSIONWe show here that mouse MIM is an actin monomer-binding protein that inhibits the nucleation of actin filaments in vitro. These activities reside in the C-terminal WH2 domain of MIM. WH2 domains are also found in many other actin monomer-interacting proteins, such as WASP, Scar, thymosin-β4, ciboulot, actobindin, and WIP/verprolin. All available data indicate that these proteins also interact with actin monomers through their WH2 domains (for recent review see Ref. 5Paunola E. Mattila P.K. Lappalainen P. FEBS Lett. 2002; 513: 92-97Google Scholar). Furthermore, at least thymosin-β4, ciboulot, and actobindin have significantly higher affinity for ATP-G-actin than for ADP-G-actin (31Hertzog M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar, M.-F. C. K.J. M. D. U. S. A. 1993; Scholar). data shows that mouse MIM affinity for ATP-G-actin is higher than its affinity for suggesting that WH2 domain has as a motif that binds is to that mouse MIM binds ATP-G-actin with higher affinity (K D = 0.06 than thymosin-β4, ciboulot, and actobindin (K D = μm) (31Hertzog M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar). For that we MIM to more actin dynamics in cells than for actin monomer-binding proteins, including and WH2 domain proteins bind to the site on the actin and with other in actin monomer-binding R. Lappalainen P. Mol. Biol. Cell. 2002; 13: D. M. Scholar, M.D. U. 1993; Scholar, D. Carlier M.F. D. J. Biol. 1998; Scholar). data show that mouse MIM has a higher affinity for ATP-G-actin (K D = 0.06 μm) than other actin monomer-binding proteins such as (K (K D = μm) and (K D = μm) (1Pollard T.D. Blanchoin L. Mullins R.D. Annu. Rev. Biophys. Biomolec. Struct. 2000; 29: 545-576Google Scholar, R. Lappalainen P. Mol. Biol. Cell. 2002; 13: Scholar). This that in the cells MIM is the of MIM is with the other the affinity of mouse MIM for ADP-G-actin (K D = 0.3 is significantly than the of (K D = μm) and (K D = that MIM significantly the and dynamics of the cellular monomer pool (1Pollard T.D. Blanchoin L. Mullins R.D. Annu. Rev. Biophys. Biomolec. Struct. 2000; 29: 545-576Google Scholar, M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; WH2 domain proteins such as actin filament whereas such as ciboulot, actobindin and WASP actin monomers the barbed ends of filaments are available I. Boujemaa R. Carlier M.F. Preat T. Cell. 2000; 102: 797-808Google Scholar, D. D'Alessio J.A. Jeng R.L. Welch M.D. Mol. Biol. Cell. 2002; 13: 4045-4059Google Scholar, M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar, M.-F. C. K.J. M. D. U. S. A. 1993; Scholar, T. J. Cell 2000; Scholar). MIM the of actin monomers in assembly and inhibits actin filament nucleation in and MIM also the end filament but can participate in barbed end filament data that MIM has on actin assembly as previously for small WH2 domain proteins and actobindin I. Boujemaa R. Carlier M.F. Preat T. Cell. 2000; 102: 797-808Google Scholar, M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar). However, because MIM is a it is to have activities that regulate the actin-modulating activities of the C-terminal WH2 Northern blot and in situ that MIM mRNA is strongly expressed in developing neurons and but absent in neurons and In adult mice, MIM is present in levels in liver, kidney, and in the Purkinje cells the small actin monomer-sequestering is expressed in several developing but only in Purkinje cells in adult R. P. E. L. I. J. 2001; Scholar). The expression of MIM in developing neurons and a role in processes are and for neurons and cells and neurons MIM and have a actin cytoskeleton and than their The of MIM in adult Purkinje cells to the and of Purkinje cell a that also in adult is interesting to that the human of MIM was identified as a gene that was present in non-metastatic but absent in metastatic bladder cancer cells (15Lee Y.-G. Macoska J.A. Korenchuk S. Pienta K.J. Neoplasia. 2002; 4: 291-294Google Scholar). in data show that MIM is strongly expressed in developing neurons and These are highly cell suggesting that MIM and cell is essential for the and of and whereas the of in cells and motility, and metastatic This an for the of MIM in metastatic bladder cancer cell (15Lee Y.-G. Macoska J.A. Korenchuk S. Pienta K.J. Neoplasia. 2002; 4: 291-294Google Scholar). MIM regulate cytoskeletal dynamics by actin only to certain regions of cells and in cells that This role is by and cell biological MIM stress fibers and in formation of abnormal actin filament structures In the it to the of MIM protein in various cell to mouse MIM have We also to small and mouse to the of MIM and in adult data show that mouse MIM binds actin monomers and regulates actin filament assembly in mammalian cell-types. MIM is a relatively it have other activities and regulate actin dynamics in a complex large WH2 domain proteins Scar, are in signaling to the actin cytoskeleton, and the activities of these proteins are regulated by relatively complex (1Pollard T.D. Blanchoin L. Mullins R.D. Annu. Rev. Biophys. Biomolec. Struct. 2000; 29: 545-576Google Scholar). MIM also a link cellular signaling pathways and actin filament assembly. In it is to that MIM also several that interact with homology domains of certain signaling In the it to the of MIM and regulate the activity and of MIM in specialized mammalian The actin cytoskeleton is central in a number of cellular processes such as motility, morphogenesis, cytokinesis, and endocytosis. The structure and dynamics of the actin cytoskeleton are spatially and temporally regulated by a large number of actin-binding proteins, whose own activities and localities are precisely regulated by various signaling pathways (1Pollard T.D. Blanchoin L. Mullins R.D. Annu. Rev. Biophys. Biomolec. Struct. 2000; 29: 545-576Google Scholar, 2Gimona M. Djinovic-Carugo K. Kranewitter W.J. Winder S.J. FEBS Lett. 2002; 513: 98-106Google Scholar, 3Van Troys M. Vandekerckhove J. Ampe C. Biochim. Biophys. Acta. 1999; 1448: 323-348Google Scholar, 4Lappalainen P. Kessels M.M. Cope J.T.V. Drubin D.G. Mol. Biol. Cell. 1998; 9: 1951-1959Google Scholar). Sequence and structural data on actin-binding proteins has revealed that many of these proteins interact with actin through a relatively small number of protein motifs. These include the calponin homology domain, the gelsolin homology domain, the actin-depolymerizing-factor homology domain, and the WASP homology 2 (WH2)1domain (for reviews see The WH2 domain is a small (∼35 residue) protein motif that interacts only with monomeric actin (5Paunola E. Mattila P.K. Lappalainen P. FEBS Lett. 2002; 513: 92-97Google Scholar, 6Symons M. Derry J.M. Karlak B.J. Jiang S. Lemahieu V. McCormick F. Francke U. Abo A. Cell. 1996; 84: 723-734Google Scholar). WH2 domains are found in many regulators of actin dynamics, including β-thymosins and ciboulot, which bind actin monomers and regulate filament assembly. β-thymosins are actin monomer-sequestering proteins, whereas ciboulot promotes actin assembly at the barbed end of the filaments (7Pantaloni D. Carlier M.-F. Cell. 1993; 75: 1007-1014Google Scholar, 8Boquet I. Boujemaa R. Carlier M.F. Preat T. Cell. 2000; 102: 797-808Google Scholar). WH2 domains are also present in more complex proteins such as WASP/Scar, verprolin/WIP, and Srv2/CAP. These are multifunctional regulators of actin dynamics that link intracellular signaling pathways to actin dynamics (5Paunola E. Mattila P.K. Lappalainen P. FEBS Lett. 2002; 513: 92-97Google Scholar). For example, WASP and Scar mediate signals from PIP2 and the small GTPases Cdc42 and Rac to the actin cytoskeleton by inducing actin assembly through activation of the Arp2/3 complex (9Machesky L.M. Insall R.H. Curr. Biol. 1998; 8: 1347-1356Google Scholar, 10Higgs H.N. Pollard T.D. J. Cell Biol. 2000; 150: 1311-1320Google Scholar, 11Prehoda K.E. Scott J.A. Mullins R.D. Lim W.A. Science. 2000; 290: 801-806Google Scholar). The WH2 domain is essential for the activity of WASP and Scar and is believed to facilitate the assembly of actin monomers to the newly formed filament ends (12Yarar D. D'Alessio J.A. Jeng R.L. Welch M.D. Mol. Biol. Cell. 2002; 13: 4045-4059Google Scholar, 13Welch M.D. Mullins R.D. Annu. Rev. Cell Dev. Biol. 2002; 18: 247-288Google Scholar). Also verprolin/WIP proteins interact with actin monomers through their WH2 domains, but the biological role of their actin monomer-binding activity is still unclear (14Thanabalu T. Munn A.L. EMBO J. 2001; 20: 6979-6989Google Scholar). We searched sequence databases for WH2 domain-containing proteins in mammals, Drosophila melanogaster,Caenorhabditis elegans, andSaccharomyces cerevisiae. In addition to the previously characterized WH2 domain proteins (β-thymosins, ciboulot, WASP, verprolin/WIP, Scar, Srv2/CAP) we identified several previously unknown WH2 domain-containing proteins (5Paunola E. Mattila P.K. Lappalainen P. FEBS Lett. 2002; 513: 92-97Google Scholar). One of these proteins is particularly interesting because it is highly homologous to a human cDNA fragment named MIM (Missing In Metastasis) that was recently identified in a differential screen for mRNAs specifically expressed in non-metastatic bladder cancer cells (15Lee Y.-G. Macoska J.A. Korenchuk S. Pienta K.J. Neoplasia. 2002; 4: 291-294Google Scholar). We show that mouse MIM is an actin monomer-binding protein that efficiently inhibits the nucleotide exchange on actin monomers and actin filament nucleation in vitro. The strong actin-modulating activities reside in the C-terminal WH2 domain of MIM. We found that MIM is strongly expressed in the developing heart, skeletal muscle, and central nervous system. In adult mouse tissues, strong expression levels are detected in liver and in certain regions of brain and kidney. Overexpression of MIM results in the disappearance of stress fibers and formation of abnormal F-actin structures in NIH 3T3 cells, suggesting that MIM regulates the dynamics of the actin monomer pool in specialized mammalian show here that mouse MIM is an actin monomer-binding protein that inhibits the nucleation of actin filaments in vitro. These activities reside in the C-terminal WH2 domain of MIM. WH2 domains are also found in many other actin monomer-interacting proteins, such as WASP, Scar, thymosin-β4, ciboulot, actobindin, and WIP/verprolin. All available data indicate that these proteins also interact with actin monomers through their WH2 domains (for recent review see Ref. 5Paunola E. Mattila P.K. Lappalainen P. FEBS Lett. 2002; 513: 92-97Google Scholar). Furthermore, at least thymosin-β4, ciboulot, and actobindin have significantly higher affinity for ATP-G-actin than for ADP-G-actin (31Hertzog M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar, M.-F. C. K.J. M. D. U. S. A. 1993; Scholar). data shows that mouse MIM affinity for ATP-G-actin is higher than its affinity for suggesting that WH2 domain has as a motif that binds is to that mouse MIM binds ATP-G-actin with higher affinity (K D = 0.06 than thymosin-β4, ciboulot, and actobindin (K D = μm) (31Hertzog M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar). For that we MIM to more actin dynamics in cells than for actin monomer-binding proteins, including and WH2 domain proteins bind to the site on the actin and with other in actin monomer-binding R. Lappalainen P. Mol. Biol. Cell. 2002; 13: D. M. Scholar, M.D. U. 1993; Scholar, D. Carlier M.F. D. J. Biol. 1998; Scholar). data show that mouse MIM has a higher affinity for ATP-G-actin (K D = 0.06 μm) than other actin monomer-binding proteins such as (K (K D = μm) and (K D = μm) (1Pollard T.D. Blanchoin L. Mullins R.D. Annu. Rev. Biophys. Biomolec. Struct. 2000; 29: 545-576Google Scholar, R. Lappalainen P. Mol. Biol. Cell. 2002; 13: Scholar). This that in the cells MIM is the of MIM is with the other the affinity of mouse MIM for ADP-G-actin (K D = 0.3 is significantly than the of (K D = μm) and (K D = that MIM significantly the and dynamics of the cellular monomer pool (1Pollard T.D. Blanchoin L. Mullins R.D. Annu. Rev. Biophys. Biomolec. Struct. 2000; 29: 545-576Google Scholar, M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; WH2 domain proteins such as actin filament whereas such as ciboulot, actobindin and WASP actin monomers the barbed ends of filaments are available I. Boujemaa R. Carlier M.F. Preat T. Cell. 2000; 102: 797-808Google Scholar, D. D'Alessio J.A. Jeng R.L. Welch M.D. Mol. Biol. Cell. 2002; 13: 4045-4059Google Scholar, M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar, M.-F. C. K.J. M. D. U. S. A. 1993; Scholar, T. J. Cell 2000; Scholar). MIM the of actin monomers in assembly and inhibits actin filament nucleation in and MIM also the end filament but can participate in barbed end filament data that MIM has on actin assembly as previously for small WH2 domain proteins and actobindin I. Boujemaa R. Carlier M.F. Preat T. Cell. 2000; 102: 797-808Google Scholar, M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar). However, because MIM is a it is to have activities that regulate the actin-modulating activities of the C-terminal WH2 Northern blot and in situ that MIM mRNA is strongly expressed in developing neurons and but absent in neurons and In adult mice, MIM is present in levels in liver, kidney, and in the Purkinje cells the small actin monomer-sequestering is expressed in several developing but only in Purkinje cells in adult R. P. E. L. I. J. 2001; Scholar). The expression of MIM in developing neurons and a role in processes are and for neurons and cells and neurons MIM and have a actin cytoskeleton and than their The of MIM in adult Purkinje cells to the and of Purkinje cell a that also in adult is interesting to that the human of MIM was identified as a gene that was present in non-metastatic but absent in metastatic bladder cancer cells (15Lee Y.-G. Macoska J.A. Korenchuk S. Pienta K.J. Neoplasia. 2002; 4: 291-294Google Scholar). in data show that MIM is strongly expressed in developing neurons and These are highly cell suggesting that MIM and cell is essential for the and of and whereas the of in cells and motility, and metastatic This an for the of MIM in metastatic bladder cancer cell (15Lee Y.-G. Macoska J.A. Korenchuk S. Pienta K.J. Neoplasia. 2002; 4: 291-294Google Scholar). MIM regulate cytoskeletal dynamics by actin only to certain regions of cells and in cells that This role is by and cell biological MIM stress fibers and in formation of abnormal actin filament structures In the it to the of MIM protein in various cell to mouse MIM have We also to small and mouse to the of MIM and in adult data show that mouse MIM binds actin monomers and regulates actin filament assembly in mammalian cell-types. MIM is a relatively it have other activities and regulate actin dynamics in a complex large WH2 domain proteins Scar, are in signaling to the actin cytoskeleton, and the activities of these proteins are regulated by relatively complex (1Pollard T.D. Blanchoin L. Mullins R.D. Annu. Rev. Biophys. Biomolec. Struct. 2000; 29: 545-576Google Scholar). MIM also a link cellular signaling pathways and actin filament assembly. In it is to that MIM also several that interact with homology domains of certain signaling In the it to the of MIM and regulate the activity and of MIM in specialized mammalian We show here that mouse MIM is an actin monomer-binding protein that inhibits the nucleation of actin filaments in vitro. These activities reside in the C-terminal WH2 domain of MIM. WH2 domains are also found in many other actin monomer-interacting proteins, such as WASP, Scar, thymosin-β4, ciboulot, actobindin, and WIP/verprolin. All available data indicate that these proteins also interact with actin monomers through their WH2 domains (for recent review see Ref. 5Paunola E. Mattila P.K. Lappalainen P. FEBS Lett. 2002; 513: 92-97Google Scholar). Furthermore, at least thymosin-β4, ciboulot, and actobindin have significantly higher affinity for ATP-G-actin than for ADP-G-actin (31Hertzog M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar, M.-F. C. K.J. M. D. U. S. A. 1993; Scholar). data shows that mouse MIM affinity for ATP-G-actin is higher than its affinity for suggesting that WH2 domain has as a motif that binds is to that mouse MIM binds ATP-G-actin with higher affinity (K D = 0.06 than thymosin-β4, ciboulot, and actobindin (K D = μm) (31Hertzog M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar). For that we MIM to more actin dynamics in cells than for actin monomer-binding proteins, including and WH2 domain proteins bind to the site on the actin and with other in actin monomer-binding R. Lappalainen P. Mol. Biol. Cell. 2002; 13: D. M. Scholar, M.D. U. 1993; Scholar, D. Carlier M.F. D. J. Biol. 1998; Scholar). data show that mouse MIM has a higher affinity for ATP-G-actin (K D = 0.06 μm) than other actin monomer-binding proteins such as (K (K D = μm) and (K D = μm) (1Pollard T.D. Blanchoin L. Mullins R.D. Annu. Rev. Biophys. Biomolec. Struct. 2000; 29: 545-576Google Scholar, R. Lappalainen P. Mol. Biol. Cell. 2002; 13: Scholar). This that in the cells MIM is the of MIM is with the other the affinity of mouse MIM for ADP-G-actin (K D = 0.3 is significantly than the of (K D = μm) and (K D = that MIM significantly the and dynamics of the cellular monomer pool (1Pollard T.D. Blanchoin L. Mullins R.D. Annu. Rev. Biophys. Biomolec. Struct. 2000; 29: 545-576Google Scholar, M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar). WH2 domain proteins such as actin filament whereas such as ciboulot, actobindin and WASP actin monomers the barbed ends of filaments are available I. Boujemaa R. Carlier M.F. Preat T. Cell. 2000; 102: 797-808Google Scholar, D. D'Alessio J.A. Jeng R.L. Welch M.D. Mol. Biol. Cell. 2002; 13: 4045-4059Google Scholar, M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar, M.-F. C. K.J. M. D. U. S. A. 1993; Scholar, T. J. Cell 2000; Scholar). MIM the of actin monomers in assembly and inhibits actin filament nucleation in and MIM also the end filament but can participate in barbed end filament data that MIM has on actin assembly as previously for small WH2 domain proteins and actobindin I. Boujemaa R. Carlier M.F. Preat T. Cell. 2000; 102: 797-808Google Scholar, M. Yarmola E.G. D. Carlier M.F. J. Biol. 2002; Scholar). However, because MIM is a it is to have activities that regulate the actin-modulating activities of the C-terminal WH2 Northern blot and in situ that MIM mRNA is strongly expressed in developing neurons and but absent in neurons and In adult mice, MIM is present in levels in liver, kidney, and in the Purkinje cells the small actin monomer-sequestering is expressed in several developing but only in Purkinje cells in adult R. P. E. L. I. J. 2001; Scholar). The expression of MIM in developing neurons and a role in processes are and for neurons and cells and neurons MIM and have a actin cytoskeleton and than their The of MIM in adult Purkinje cells to the and of Purkinje cell a that also in adult is interesting to that the human of MIM was identified as a gene that was present in non-metastatic but absent in metastatic bladder cancer cells (15Lee Y.-G. Macoska J.A. Korenchuk S. Pienta K.J. Neoplasia. 2002; 4: 291-294Google Scholar). in data show that MIM is strongly expressed in developing neurons and These are highly cell suggesting that MIM and cell is essential for the and of and whereas the of in cells and motility, and metastatic This an for the of MIM in metastatic bladder cancer cell (15Lee Y.-G. Macoska J.A. Korenchuk S. Pienta K.J. Neoplasia. 2002; 4: 291-294Google Scholar). MIM regulate cytoskeletal dynamics by actin only to certain regions of cells and in cells that This role is by and cell biological MIM stress fibers and in formation of abnormal actin filament structures In the it to the of MIM protein in various cell to mouse MIM have We also to small and mouse to the of MIM and in adult data show that mouse MIM binds actin monomers and regulates actin filament assembly in mammalian cell-types. MIM is a relatively it have other activities and regulate actin dynamics in a complex large WH2 domain proteins Scar, are in signaling to the actin cytoskeleton, and the activities of these proteins are regulated by relatively complex (1Pollard T.D. Blanchoin L. Mullins R.D. Annu. Rev. Biophys. Biomolec. Struct. 2000; 29: 545-576Google Scholar). MIM also a link cellular signaling pathways and actin filament assembly. In it is to that MIM also several that interact with homology domains of certain signaling In the it to the of MIM and regulate the activity and of MIM in specialized mammalian
Mattila et al. (Fri,) reported a other. Mouse MIM protein was evaluated on Actin monomer binding and filament nucleation. Mouse MIM binds ATP-G-actin with higher affinity (KD = 0.06 μm) than ADP-G-actin (KD = 0.3 μm) via its C-terminal WH2 domain, inhibiting actin filament nucleation in vitro.