Formation of sarcoglycan complex with differentiation in cultured myocytes

The sarcoglycan complex consists of four transmembrane protein subunits. Mu tation of any one of the genes encoding these four subunits causes complete loss or marked decrease in expression of the whole complex, resulting in t he phenotype of Duchenne-like autosomal recessive muscular dystrophy, terme d sarcoglycanopathy. As the basis for understanding this process, we examin ed how the sarcoglycan complex is formed and associates with other proteins during myogenic differentiation, using a myogenic cell line. Accumulation of the sarcoglycan subunits and formation of the sarcoglycan complex were a ccomplished with myotube formation. In protein transport inhibition experim ents with blefeldin A, we found that the sarcoglycan complex is formed in t he endoplasmic reticulum and then associates with the dystroglycan complex and sarcospan en route from the Golgi apparatus to the cell surface. In ear ly myotubes, limited kinds of incomplete sarcoglycan complexes were observe d. Their analyses would provide information on the possible patterns of for mation of the sarcoglycan complex.