Nuclear and nuclear envelope localization of dystrophin Dp71 and dystrophin‐associated proteins (DAPs) in the C2C12 muscle cells: DAPs nuclear localization is modulated during myogenesis

Dystrophin and dystrophin‐associated proteins (DAPs) form a complex around the sarcolemma, which gives stability to the sarcolemma and leads signal transduction. Recently, the nuclear presence of dystrophin Dp71 and DAPs has been revealed in different non‐muscle cell types, opening the possibility that these proteins could also be present in the nucleus of muscle cells. In this study, we analyzed by Immunofluorescence assays and Immunoblotting analysis of cell fractions the subcellular localization of Dp71 and DAPs in the C2C12 muscle cell line. We demonstrated the presence of Dp71, α‐sarcoglycan, α‐dystrobrevin, β‐dystroglycan and α‐syntrophin not only in plasma membrane but also in the nucleus of muscle cells. In addition, we found by Immunoprecipitation assays that these proteins form a nuclear complex. Interestingly, myogenesis modulates the presence and/or relative abundance of DAPs in the plasma membrane and nucleus as well as the composition of the nuclear complex. Finally, we demonstrated the presence of Dp71, α‐sarcoglycan, β‐dystroglycan, α‐dystrobrevin and α‐syntrophin in the C2C12 nuclear envelope fraction. Interestingly, α‐sarcoglycan and β‐dystroglycan proteins showed enrichment in the nuclear envelope, compared with the nuclear fraction, suggesting that they could function as inner nuclear membrane proteins underlying the secondary association of Dp71 and the remaining DAPs to the nuclear envelope. Nuclear envelope localization of Dp71 and DAPs might be involved in the nuclear envelope‐associated functions, such as nuclear structure and modulation of nuclear processes. J. Cell. Biochem. 105: 735–745, 2008. © 2008 Wiley‐Liss, Inc.