Bidirectional Signaling between Sarcoglycans and the Integrin Adhesion System in Cultured L6 Myocytes

Abstract

The rat L6 skeletal muscle cell line was used to study expression of the dystrophin-containing glycoprotein complex and its interaction with the integrin system involved in the cell-matrix adhesion reaction. A complex of dystrophin and its associated proteins was fully expressed in L6 myotubes, from which anti-dystrophin or anti-α-sarcoglycan co-precipitated integrin α5β1 and other focal adhesion-associated proteins vinculin, talin, paxillin, and focal adhesion kinase. Immunostaining and confocal microscopy revealed that dystrophin, α-sarcoglycan, integrin α5β1, and vinculin exhibited overlapping distribution in the sarcolemma, especially at focal adhesion-like, spotty structures. Adhesion of cells to fibronectin- or collagen type I-coated dishes resulted in induction of tyrosine phosphorylation of α- and γ-sarcoglycans but not β-sarcoglycan. The same proteins were also tyrosine-phosphorylated when L6 cells in suspension were exposed to Arg-Gly-Asp-Ser peptide. All of these tyrosine phosphorylations were inhibited by herbimycin A. On the other hand, treatment of L6 myotubes with α- and γ-sarcoglycan antisense oligodeoxynucleotides resulted in complete disappearance of α- and γ-sarcoglycans and in significant reduction of levels of the associated focal adhesion proteins, which caused about 50% reduction of cell adhesion. These results indicate the existence of bidirectional communication between the dystrophin-containing complex and the integrin adhesion system in cultured L6 myocytes. The rat L6 skeletal muscle cell line was used to study expression of the dystrophin-containing glycoprotein complex and its interaction with the integrin system involved in the cell-matrix adhesion reaction. A complex of dystrophin and its associated proteins was fully expressed in L6 myotubes, from which anti-dystrophin or anti-α-sarcoglycan co-precipitated integrin α5β1 and other focal adhesion-associated proteins vinculin, talin, paxillin, and focal adhesion kinase. Immunostaining and confocal microscopy revealed that dystrophin, α-sarcoglycan, integrin α5β1, and vinculin exhibited overlapping distribution in the sarcolemma, especially at focal adhesion-like, spotty structures. Adhesion of cells to fibronectin- or collagen type I-coated dishes resulted in induction of tyrosine phosphorylation of α- and γ-sarcoglycans but not β-sarcoglycan. The same proteins were also tyrosine-phosphorylated when L6 cells in suspension were exposed to Arg-Gly-Asp-Ser peptide. All of these tyrosine phosphorylations were inhibited by herbimycin A. On the other hand, treatment of L6 myotubes with α- and γ-sarcoglycan antisense oligodeoxynucleotides resulted in complete disappearance of α- and γ-sarcoglycans and in significant reduction of levels of the associated focal adhesion proteins, which caused about 50% reduction of cell adhesion. These results indicate the existence of bidirectional communication between the dystrophin-containing complex and the integrin adhesion system in cultured L6 myocytes. Several classes of cell adhesion receptors, including integrins, dystroglycan, cadherins, and members of the immunoglobulin family, are coexpressed by skeletal muscle and presumably play critical roles during skeletal muscle differentiation and development (see Ref. 1McDonald K.A. Horwitz A.F. Knudsen K.A. Semin. Dev. Biol. 1995; 6: 105-116Crossref Scopus (37) Google Scholar for review). Integrins form a large family of heterodimeric transmembrane proteins with different α and β subunits (2Hynes R.O. Cell. 1992; 69: 11-25Abstract Full Text PDF PubMed Scopus (9013) Google Scholar). The ligands of the integrins can be components of the extracellular matrix or other integral membrane proteins, such as VCAM-1. Previous studies suggest that different integrins may play specific roles in different developmental and cellular phenomena. The β1 integrin subfamily, with its different α subunits, is a major group of integrins expressed in muscle cells and has been shown to be required for myoblast differentiation and myotube formation (1McDonald K.A. Horwitz A.F. Knudsen K.A. Semin. Dev. Biol. 1995; 6: 105-116Crossref Scopus (37) Google Scholar, 3Menko A.S. Boettiger D. Cell. 1987; 51: 51-57Abstract Full Text PDF PubMed Scopus (309) Google Scholar). A large number of different integrin α subunits are expressed in developing muscle cells, and some of them localize in unique functional cellular regions and seem to play distinct roles in regulation of myogenesis, although their precise functions remain to be clarified (1McDonald K.A. Horwitz A.F. Knudsen K.A. Semin. Dev. Biol. 1995; 6: 105-116Crossref Scopus (37) Google Scholar, 4McDonald K.A. Lakonishok M. Horwitz A.F. J. Cell. Sci. 1995; 108: 2573-2581PubMed Google Scholar, 5Sastry S.K. Lakonishok M. Thomas D.A. Muschler J. Horwitz A.F. J. Cell Biol. 1996; 133: 169-184Crossref PubMed Scopus (173) Google Scholar). Myogenic cells associate with extracellular matrix, which is advantageous for cell terminal differentiation. The extracellular matrix-integrin interaction occurs at various cytoskeletal-sarcolemmal linkages, such as focal adhesion-like structures, myotendinous and neuromuscular junctions, and the costameres (1McDonald K.A. Horwitz A.F. Knudsen K.A. Semin. Dev. Biol. 1995; 6: 105-116Crossref Scopus (37) Google Scholar, 4McDonald K.A. Lakonishok M. Horwitz A.F. J. Cell. Sci. 1995; 108: 2573-2581PubMed Google Scholar, 6Terracio L. Gullberg D. Rubin K. Craig S. Borg T.M. Anat. Rec. 1989; 223: 62-71Crossref PubMed Scopus (62) Google Scholar). At the focal adhesions present in cultured cells, integrins cluster and associate with many cytoskeletal proteins, such as talin, vinculin, paxillin, and α-actinin, as well as FAK 1The abbreviations used are: FAK, focal adhesion kinase; DAP, dystrophin-associated protein; ODN, oligodeoxynucleotide; DMEM, Dulbecco's modified Eagle's medium; FCS, fetal calf serum; PBS, phosphate-buffered saline; BSA, bovine serum albumin. and other protein kinases (7Jockusch B.M. Bubeck P. Giehl K. Kroemker M. Moschner J. Rothkegel M. Rudiger M. Schluter K. Stanke G. Winkler J. Annu. Rev. Cell Dev. Biol. 1995; 11: 379-416Crossref PubMed Scopus (430) Google Scholar, 8Miyamato S. Teramoto H. Caso O.A. Gutkind J.S. Burbelo P.D. Akiyama S.K. Yamada K.M. J. Cell Biol. 1995; 131: 791-805Crossref PubMed Scopus (1104) Google Scholar, 9Schwartz M.A. Schaller M.D. Ginsberg M.H. Annu. Rev. Cell Dev. Biol. 1995; 11: 549-599Crossref PubMed Scopus (1469) Google Scholar). The focal adhesion complex is the major site of actin filament attachment. Recent evidence indicates that assembly of the focal complex requires both the engagement of integrins with extracellular matrix and the integrin activation by intracellular signaling, although the physiological mechanism of the latter is largely unknown (9Schwartz M.A. Schaller M.D. Ginsberg M.H. Annu. Rev. Cell Dev. Biol. 1995; 11: 549-599Crossref PubMed Scopus (1469) Google Scholar). Integrin occupancy with ligands and clustering have been shown to trigger tyrosine phosphorylation of several intracellular proteins, including FAK, paxillin, tensin, and mitogen-activated protein kinase (2Hynes R.O. Cell. 1992; 69: 11-25Abstract Full Text PDF PubMed Scopus (9013) Google Scholar, 7Jockusch B.M. Bubeck P. Giehl K. Kroemker M. Moschner J. Rothkegel M. Rudiger M. Schluter K. Stanke G. Winkler J. Annu. Rev. Cell Dev. Biol. 1995; 11: 379-416Crossref PubMed Scopus (430) Google Scholar, 9Schwartz M.A. Schaller M.D. Ginsberg M.H. Annu. Rev. Cell Dev. Biol. 1995; 11: 549-599Crossref PubMed Scopus (1469) Google Scholar). Recent evidence suggests that tyrosine phosphorylation of FAK and other focal adhesion proteins is not required for focal adhesion formation but is important for the other integrin-induced signalings, such as control of cell growth (10Gilmore A.P. Romer L.H. Mol. Biol. Cell. 1996; 7: 1209-1224Crossref PubMed Scopus (461) Google Scholar). However, assembly of the focal adhesion complex can be inhibited by tyrosine kinase inhibitors (8Miyamato S. Teramoto H. Caso O.A. Gutkind J.S. Burbelo P.D. Akiyama S.K. Yamada K.M. J. Cell Biol. 1995; 131: 791-805Crossref PubMed Scopus (1104) Google Scholar, 11Burridge K. Turner C.E. Romer L.H. J. Cell Biol. 1992; 119: 893-904Crossref PubMed Scopus (1182) Google Scholar). Dystroglycan, which exists as a noncovalently linked complex of α- and β-subunits, is another important cell adhesion receptor that links the extracellular matrix with the actin cytoskeleton (12Ibraghimov-Beskrovaya O. Ervasti J.M. Leveille C.J. Slaughter A. Sernett S.W. Campbell K.P. Nature. 1992; 355: 696-703Crossref PubMed Scopus (1195) Google Scholar, 13Tinsley J.M. Blake D.J. Zuelling R.A. Davies K.E. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 8307-8313Crossref PubMed Scopus (185) Google Scholar, 14Campbell K.P. Cell. 1995; 80: 675-679Abstract Full Text PDF PubMed Scopus (759) Google Scholar). In skeletal muscle cells, it forms a tight complex with dystrophin together with other dystrophin-associated proteins (DAPs) including α-, β-, γ- and δ-sarcoglycans, the 25-kDa protein, and syntrophins (13Tinsley J.M. Blake D.J. Zuelling R.A. Davies K.E. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 8307-8313Crossref PubMed Scopus (185) Google Scholar, 14Campbell K.P. Cell. 1995; 80: 675-679Abstract Full Text PDF PubMed Scopus (759) Google Scholar, 16Roberds S.L. Leturcq M. M. J.S. Campbell K.P. Cell. 1994; Full Text PDF PubMed Scopus (430) Google Scholar, O. Slaughter M. C.E. J.S. Campbell K.P. 1995; 11: PubMed Scopus (430) Google Scholar, S. M. H. L. J.M. 1995; PubMed Scopus Google Scholar, G. A. L. S. G. G. Mol. 1996; PubMed Scopus Google Scholar, D. Leveille C.J. Slaughter Campbell K.P. J. Biol. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). is expressed in cells, as well as in are expressed in muscle cells (12Ibraghimov-Beskrovaya O. Ervasti J.M. Leveille C.J. Slaughter A. Sernett S.W. Campbell K.P. Nature. 1992; 355: 696-703Crossref PubMed Scopus (1195) Google Scholar, P.D. S. J. Biol. Full Text PDF PubMed Google Scholar, 16Roberds S.L. Leturcq M. M. J.S. Campbell K.P. Cell. 1994; Full Text PDF PubMed Scopus (430) Google Scholar, O. Slaughter M. C.E. J.S. Campbell K.P. 1995; 11: PubMed Scopus (430) Google Scholar, S. M. H. L. J.M. 1995; PubMed Scopus Google Scholar, G. A. L. S. G. G. Mol. 1996; PubMed Scopus Google Scholar, D. Leveille C.J. Slaughter Campbell K.P. J. Biol. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). The of the complex to be for the of muscle cells, of the complex to a in dystrophin or of the has been to various forms of (13Tinsley J.M. Blake D.J. Zuelling R.A. Davies K.E. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 8307-8313Crossref PubMed Scopus (185) Google Scholar, 14Campbell K.P. Cell. 1995; 80: 675-679Abstract Full Text PDF PubMed Scopus (759) Google Scholar, 16Roberds S.L. Leturcq M. M. J.S. Campbell K.P. Cell. 1994; Full Text PDF PubMed Scopus (430) Google Scholar, O. Slaughter M. C.E. J.S. Campbell K.P. 1995; 11: PubMed Scopus (430) Google Scholar, S. M. H. L. J.M. 1995; PubMed Scopus Google G. M. A. L. M. 1996; PubMed Scopus Google Scholar). seem to be and as important as At other components of the is about the functional and roles of including their interaction with other cellular In H. M. 1996; PubMed Scopus Google have evidence that the complex is associated with the focal adhesion assembly proteins, such as the integrin β1 vinculin, and FAK in cells, a muscle cell have also shown that of by the antisense treatment results in a significant of adhesion to the by these In that α- or γ-sarcoglycans were tyrosine-phosphorylated when rat skeletal L6 cells were to the extracellular On the other hand, treatment of these cells with antisense α- or γ-sarcoglycan the associated focal adhesion proteins and inhibited cell adhesion. The results indicate the existence of bidirectional communication between the complex and the integrin adhesion system in these cultured dystrophin integrin β1 vinculin and were and were from was a from M. J. Cell. Biol. 1987; PubMed Scopus Google Scholar). integrin α5β1 and integrin were from and which actin was a from K. J. Cell Biol. PubMed Scopus Google Scholar). A the of to was as H. M. J. Mol. Cell. 1996; Full Text PDF PubMed Scopus Google Scholar). of proteins of skeletal muscle and of skeletal muscle γ-sarcoglycan was also H. M. M. Biol. PubMed Scopus Google Scholar). These which were and proteins as S. J. M. J. Biol. 1994; Full Text PDF PubMed Google proteins of the for in the of L6 cell (see L6 rat skeletal were dishes in with FCS, and of cells were to form used these cells for in cell adhesion these cells were from dishes by with and with BSA, and with for at a were dishes with collagen or and at for the (see with BSA, cells were with The cells to as in were in suspension for In some cells in suspension were with Arg-Gly-Asp-Ser were with and for with and The were at for at and the were with of protein for at a the were with for at and with of protein for The were with the of and and in of for The were to a or as A. M. H. M. J. Google Scholar). In some used that was for and the and for and (see proteins were to with and with and with the system as A. M. H. M. J. Google Scholar). of was as H. M. M. PubMed Scopus Google Scholar). The were and antisense ODN, of rat antisense ODN, of rat γ-sarcoglycan antisense ODN, of rat γ-sarcoglycan and control with a in for L6 cells were with antisense or control in the of but in the of for were with and in and for The latter was to cells to for a of were for expression of α-, β-, and γ-sarcoglycans by L6 cells cultured were in for at and in for at with PBS, cells were with a for at and with were with of the for at anti-α-sarcoglycan anti-dystrophin β1 or α5β1 with cells were with or for at and with with a of and and cells were with a of and with a of the and were by confocal microscopy a system with a The rat L6 skeletal muscle cell line has been used as a for in L6 with other to form myotubes and skeletal muscle proteins D. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, A. J. Biol. 1992; Full Text PDF PubMed Google Scholar). specific the expression and distribution of the components of the complex in L6 cells that been cultured dishes for The from L6 cells with anti-dystrophin proteins by dystrophin, and α-, β-, and γ-sarcoglycans was by In the same the proteins with focal adhesion-associated proteins, such as integrin α5β1, vinculin, talin, and FAK also also a protein with not that the with proteins with the components of the complex The of focal adhesion proteins from cell with anti-dystrophin were and for integrin α5β1, vinculin, talin, and FAK, as by of the proteins with anti-dystrophin and in the the of dystrophin and were the cell and anti-dystrophin of the dystrophin not when L6 cells were from dishes and in suspension for the proteins with focal adhesion proteins or in the dystrophin although levels of dystrophin and not of antisense adhesion of L6 cells and expression of focal adhesion-associated L6 cells were for with of or antisense and dishes at a of cells in for the of Cell adhesion were as the from from cells with or antisense antisense antisense or γ-sarcoglycan antisense were to with anti-dystrophin by with specific the other cytoskeletal proteins, such as integrin and not the components of the complex from L6 cells A and not integrin and were not in the dystrophin A was not in the integrin On the other hand, a of actin was in the dystrophin from and cells actin to be that is to dystrophin, dystrophin is to be protein (13Tinsley J.M. Blake D.J. Zuelling R.A. Davies K.E. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 8307-8313Crossref PubMed Scopus (185) Google Scholar, 14Campbell K.P. Cell. 1995; 80: 675-679Abstract Full Text PDF PubMed Scopus (759) Google Scholar, M. R.A. J. 1992; PubMed Scopus Google Scholar). the of actin was not cell and about of the actin was present in the with anti-dystrophin not for these with anti-dystrophin the but and of and cells were in and and were in the same of proteins with protein was to about but anti-dystrophin or integrin was to of the proteins that were in the the (see a in the of protein not of these it that the dystrophin not large cytoskeletal the of specific interaction of the complex with focal adhesion-associated of proteins by dystrophin, α-sarcoglycan, integrin α5β1, and vinculin in L6 cells dishes by and confocal In a cell at the α5β1 or anti-dystrophin the A and in a cell at the spotty of cell was with anti-dystrophin cells with anti-α-sarcoglycan and In a cell at the from both at many spotty although not at some other structures. These spotty with may be to focal adhesions in (7Jockusch B.M. Bubeck P. Giehl K. Kroemker M. Moschner J. Rothkegel M. Rudiger M. Schluter K. Stanke G. Winkler J. Annu. Rev. Cell Dev. Biol. 1995; 11: 379-416Crossref PubMed Scopus (430) Google Scholar). the of a cell was of was in cells the from anti-α-sarcoglycan was in its in the cell and the of from anti-α-sarcoglycan and was in these cells, the cell the was also tyrosine phosphorylation of proteins in L6 cells in to cell adhesion. L6 cells dishes for exhibited a of tyrosine phosphorylation of proteins, with and of the in the to be FAK (see which is with with cells K. Turner C.E. Romer L.H. J. Cell Biol. 1992; 119: 893-904Crossref PubMed Scopus (1182) Google Scholar, L. Schaller M. J. Biol. Full Text PDF Google Scholar). the proteins from L6 cells with anti-dystrophin or anti-α-sarcoglycan were In proteins of and were that are α- and γ-sarcoglycans These proteins, were not tyrosine-phosphorylated in L6 cells also A phosphorylation of and proteins were not in the with integrin that α- and γ-sarcoglycans are tyrosine-phosphorylated in L6 cells, the of treatment with antisense tyrosine phosphorylation of the and treatment of L6 cells with α-, β-, or γ-sarcoglycan antisense for resulted in complete disappearance of the and proteins from the dystrophin and the same the and with also and In or antisense not tyrosine phosphorylation of the and proteins and antisense not the of components of the complex other the in the dystrophin not that not the A the of tyrosine phosphorylation of α- and γ-sarcoglycans as well as of the protein by in L6 cells The of cell to dishes with other are also shown cell was not in α- or γ-sarcoglycan in the or in the protein by in the FAK cell tyrosine phosphorylation of the protein by was significant at a at or In of α- and γ-sarcoglycans was and of the at although it levels at about of L6 cells to dishes at In cell to collagen type and dishes was A that α- and γ-sarcoglycans were tyrosine-phosphorylated to a in cells for fibronectin- or However, tyrosine phosphorylation of these proteins was in cells In the from cells the protein by and its tyrosine phosphorylation were with from cells and of and tyrosine phosphorylation of the protein by in the FAK from the same cells were also with from cells and On the other hand, the protein by was not in the from cells the of cell tyrosine phosphorylation of is to be by a of integrins (2Hynes R.O. Cell. 1992; 69: 11-25Abstract Full Text PDF PubMed Scopus (9013) Google Scholar, M.D. Proc. Natl. Acad. Sci. U. S. A. Scopus Google Scholar). phosphorylation of α- and as well as of the protein by was when L6 cells in suspension were exposed to However, tyrosine phosphorylation of was not not treatment of L6 cells with herbimycin a tyrosine kinase resulted in of the or cell tyrosine phosphorylation of α- and γ-sarcoglycans and the protein with that the phosphorylation was by a herbimycin tyrosine kinase. and the protein with in the by anti-α-sarcoglycan or from the cells not In the shown in adhesion of L6 cells with of antisense that adhesion to dishes was inhibited by about 50% in cells with α- or γ-sarcoglycan antisense for In these cells, tyrosine phosphorylation of the protein with was also to and of with not adhesion of L6 cells, treatment with antisense cell adhesion that these antisense not the actin cytoskeleton of L6 the of antisense levels of some focal adhesion proteins in cell by with antisense α-, β-, and γ-sarcoglycan for resulted in a of to and of the for the cells, However, the same treatment caused a in levels of integrin vinculin, talin, and FAK in the cell On the other hand, integrin β1 vinculin, talin, and FAK in the dystrophin to and of in the antisense cells and to and of in γ-sarcoglycan antisense cells or antisense ODN, not the levels of these proteins in the dystrophin The of of integrin in the dystrophin was not by with of these antisense In have several of evidence that the complex in cultured rat L6 myotubes has specific bidirectional with the α5β1 integrin adhesion anti-dystrophin or anti-α-sarcoglycan co-precipitated integrin α5β1 and other focal adhesion-associated proteins talin, paxillin, and together with the components of the complex A not other cytoskeletal proteins, such as integrin and actin A and integrin or co-precipitated the components of the although integrin and not them and study confocal microscopy revealed that and vinculin exhibited overlapping distribution in the sarcolemma, especially at the spotty in the cell when L6 cells were dishes Adhesion of L6 cells to or collagen type resulted in induction of tyrosine phosphorylation of α- and γ-sarcoglycans phosphorylation of these proteins was when L6 cells in suspension were exposed to that with integrins (2Hynes R.O. Cell. 1992; 69: 11-25Abstract Full Text PDF PubMed Scopus (9013) Google Scholar, M.D. Proc. Natl. Acad. Sci. U. S. A. Scopus Google treatment of L6 cells with α- and γ-sarcoglycan antisense resulted in complete disappearance of α- and γ-sarcoglycans and significant reduction of the associated focal adhesion proteins which caused about 50% reduction of cell adhesion The integrin system involved in the bidirectional interaction with the complex in L6 cells to be that is in the cell-matrix of the complex with focal adhesion-associated proteins is required for the tyrosine phosphorylation of α- and In L6 cells in α- and γ-sarcoglycans and FAK were not and anti-dystrophin or anti-α-sarcoglycan not FAK, vinculin, and from these cells, although co-precipitated some integrin α5β1 and However, when cells in suspension been with α- and γ-sarcoglycans and FAK were and their tyrosine phosphorylation as in cells and On the other hand, tyrosine phosphorylation of α- and γ-sarcoglycans was not in cells although a of FAK was to be present in the study revealed a reduction of the of from anti-α-sarcoglycan and at the of a cell of proteins to the focal adhesion-like, spotty to be required for the phosphorylation of the of integrin α5β1, vinculin, talin, or FAK co-precipitated with anti-dystrophin was about of the of that was present in the cell (see that of these proteins are associated with the be to existence in L6 cells of of integrin α5β1 and other focal adhesion proteins with the be that of these focal adhesion proteins with the dystrophin complex occurs at the cell dystrophin, α-sarcoglycan, α5β1, and vinculin were present at the in both the and of the cell of and vinculin were in both of these membrane with at the of the cell At the of the interaction between these proteins is In and other cells, formation of the focal adhesion and activation of FAK, a of a family of distinct tyrosine kinases (9Schwartz M.A. Schaller M.D. Ginsberg M.H. Annu. Rev. Cell Dev. Biol. 1995; 11: 549-599Crossref PubMed Scopus (1469) Google Scholar, A. 1995; PubMed Scopus Google Scholar). its tyrosine FAK to of the latter to focal adhesion M.D. Mol. Cell Biol. 1994; PubMed Scopus Google Scholar). In that is to tyrosine α- and γ-sarcoglycans in phosphorylation of in to cell adhesion in L6 cells is to be by FAK or tyrosine such as a of the family of are membrane proteins a tight which is associated with the dystrophin, and other proteins to form the complex (see large extracellular and O. Slaughter M. C.E. J.S. Campbell K.P. 1995; 11: PubMed Scopus (430) Google Scholar, S. M. H. L. J.M. 1995; PubMed Scopus Google Scholar, G. A. L. S. G. G. Mol. 1996; PubMed Scopus Google Scholar, D. Leveille C.J. Slaughter Campbell K.P. J. Biol. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar, S.L. O. Campbell K.P. J. Biol. Full Text PDF PubMed Google Scholar). that cell adhesion tyrosine phosphorylation of α- and γ-sarcoglycans but not and that with γ-sarcoglycan and and tyrosine in the at a to the transmembrane S.L. O. Campbell K.P. J. Biol. Full Text PDF PubMed Google γ-sarcoglycan has tyrosine S. M. H. L. J.M. 1995; PubMed Scopus Google Scholar). in be in L6 cells, although is for the phosphorylation site in is also the of tyrosine phosphorylation of α- and γ-sarcoglycans with to their or The antisense α- or γ-sarcoglycan for inhibited adhesion of L6 cells to by about 50% antisense α- or γ-sarcoglycan from these cells although expression as well as the of dystrophin and other to form a tight were not by the treatment (see these integrin β1 vinculin, talin, and FAK co-precipitated with anti-dystrophin were by although levels of these proteins in the cell were not and In antisense cell as well as the of the complex with focal adhesion α- and γ-sarcoglycans may be involved in L6 cell adhesion by with focal adhesion-associated in skeletal muscle of with various forms of in of the in the of the other from the S.L. Leturcq M. M. J.S. Campbell K.P. Cell. 1994; Full Text PDF PubMed Scopus (430) Google Scholar, O. Slaughter M. C.E. J.S. Campbell K.P. 1995; 11: PubMed Scopus (430) Google Scholar, S. M. H. L. J.M. 1995; PubMed Scopus Google Scholar, G. M. A. L. M. 1996; PubMed Scopus Google Scholar). are in to the of the of of the protein the of the complex in L6 may in that or in the complex in cultured L6 cells skeletal of dystrophin in cell has been and PubMed Scopus Google that dystrophin and a protein, which is by are to focal adhesion-like in cultured muscle In Lakonishok M. J. Horwitz A.F. Dev. Biol. 1992; PubMed Scopus Google overlapping of α5β1 integrin and dystrophin in a the of the cultured skeletal myotube during muscle have also that some focal adhesion-associated proteins are co-precipitated with the complex from muscle cell line cells that have been cultured differentiation H. M. 1996; PubMed Scopus Google Scholar). On the other hand, in in which dystrophin is not a protein is a of the membrane and of extracellular ligands to integrin has been shown to with other membrane proteins including and vinculin, to the from the S. J. Biol. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). The bidirectional interaction between the complex and the system in cultured muscle cells suggests that it play important in the regulation of the of adhesion Integrins are the adhesion and is about the mechanism by which the bidirectional of the membrane (2Hynes R.O. Cell. 1992; 69: 11-25Abstract Full Text PDF PubMed Scopus (9013) Google Scholar, 7Jockusch B.M. Bubeck P. Giehl K. Kroemker M. Moschner J. Rothkegel M. Rudiger M. Schluter K. Stanke G. Winkler J. Annu. Rev. Cell Dev. Biol. 1995; 11: 379-416Crossref PubMed Scopus (430) Google Scholar, 9Schwartz M.A. Schaller M.D. Ginsberg M.H. Annu. Rev. Cell Dev. Biol. 1995; 11: 549-599Crossref PubMed Scopus (1469) Google Scholar). In is about the of the for which is a transmembrane adhesion seem to be important for the of the complex in muscle However, has been for the interaction of with other cellular is to is a bidirectional interaction between the complex and the in the skeletal Previous studies of muscle have that dystroglycan, dystrophin, integrin β1 vinculin, talin, and localize to the of costameres that of the to the L. Gullberg D. Rubin K. Craig S. Borg T.M. Anat. Rec. 1989; 223: 62-71Crossref PubMed Scopus (62) Google Scholar, 1996; PubMed Scopus Google Scholar, Craig Proc. Natl. Acad. Sci. U. S. A. 80: PubMed Scopus Google Scholar, J. Cell Biol. 1992; PubMed Scopus Google Scholar). S. and K. for their of