Bidirectional Signaling between Sarcoglycans and the Integrin Adhesion System in Cultured L6 Myocytes*
- From the Department of Molecular Physiology, National Cardiovascular Center Research Institute, Fujishiro-dai 5-7, Suita, Osaka 565, Japan
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.
Footnotes
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↵* This work was supported by Grant-in-aid for Scientific Research on Priority Areas 343 from the Ministry of Education, Science and Culture, Research Grant for Cardiovascular Diseases 8A-1 from the Ministry of Health and Welfare of Japan, and a grant from Sankyo Life Science Foundation.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed. Tel.: 81-6-833-5012; Fax: 81-6-872-7485.
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↵1 The 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.
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↵2 T. Yoshida, unpublished observation.
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- Received May 19, 1997.
- Revision received October 17, 1997.
- The American Society for Biochemistry and Molecular Biology, Inc.
