title: Dystroglycan is not required for localization of dystrophin, syntrophin, and neuronal nitric-oxide synthase at the sarcolemma but regulates integrin alpha 7B expression and caveolin-3 distribution.
abstract: Dystroglycan is part of the dystrophin-associated protein complex, which joins laminin in the extracellular matrix to dystrophin within the subsarcolemmal cytoskeleton. We have investigated how mutations in the components of the laminin-dystroglycan-dystrophin axis affect the organization and expression of dystrophin-associated proteins by comparing mice mutant for merosin (alpha(2)-laminin, dy), dystrophin (mdx), and dystroglycan (Dag1) using immunohistochemistry and immunoblots. We report that syntrophin and neuronal nitric-oxide synthase are depleted in muscle fibers lacking both dystrophin and dystroglycan. Some fibers deficient in dystroglycan, however, localize dystrophin at the cell surface at levels similar to that in wild-type muscle. Nevertheless, these fibers have signs of degeneration/regeneration including increased cell surface permeability and central nuclei. In these fibers, syntrophin and nitric-oxide synthase are also localized to the plasma membrane, whereas the sarcoglycan complex is disrupted. These results suggest a mechanism of membrane attachment for dystrophin independent of dystroglycan and that the interaction of sarcoglycans with dystrophin requires dystroglycan. The distribution of caveolin-3, a muscle-specific component of caveolae recently found to bind dystroglycan, was affected in dystroglycan- and dystrophin-deficient mice. We also examined alternative mechanisms of cell-extracellular matrix attachment to elucidate how the muscle basement membrane may subsist in the absence of dystroglycan, and we found the alpha(7B) splice variant of the alpha(7) integrin receptor subunit to be up-regulated. These results support the possibility that alpha(7B) integrin compensates in mediating cell-extracellular matrix attachment but cannot rescue the dystrophic phenotype.
authors.affiliation: Center for Research in Neuroscience, McGill University and Montreal General Hospital Research Institute, Québec H3G 1A4, Canada.
authors.forename: Patrice D
authors.initials: PD
authors.lastname: Côté
authors.forename: Hakima
authors.initials: H
authors.lastname: Moukhles
authors.forename: Salvatore
authors.initials: S
authors.lastname: Carbonetto
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis* / Q000235:genetics; D051244:Caveolin 3; D022461:Caveolins / Q000096:biosynthesis*; D003402:Creatine Kinase / Q000097:blood / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D003902:Detergents / Q000494:pharmacology; D049030:Dystroglycans; D016189:Dystrophin / Q000378:metabolism*; D049029:Dystrophin-Associated Proteins; D004622:Embryo, Mammalian / Q000166:cytology; D005091:Exons; D005109:Extracellular Matrix / Q000378:metabolism; D015151:Immunoblotting; D007150:Immunohistochemistry; D039001:Integrin alpha Chains; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D008854:Microscopy, Electron; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D009154:Mutation; D009474:Neurons / Q000201:enzymology*; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D017830:Octoxynol / Q000494:pharmacology; D010641:Phenotype; D011485:Protein Binding; D012508:Sarcolemma / Q000378:metabolism*; D013234:Stem Cells / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D015703:Antigens, CD; C495548:Cav3 protein, mouse; D051244:Caveolin 3; D022461:Caveolins; D003598:Cytoskeletal Proteins; C483081:DAG1 protein, human; D003902:Detergents; D016189:Dystrophin; D049029:Dystrophin-Associated Proteins; D039001:Integrin alpha Chains; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009124:Muscle Proteins; C085725:integrin alpha7; C091824:syntrophin; D049030:Dystroglycans; D017830:Octoxynol; D019001:Nitric Oxide Synthase; D003402:Creatine Kinase