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 resuited 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 tyro sine 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 αand 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.