Fig. 7. Failed targeting of Src to the nucleus and altered Src activation in myotubes expressing the TFT mutant caveolin-3. (A) Control myotubes and myotubes expressing the TFT mutation were analyzed immunocytochemically for the cellular distribution of Src. While Src was present diffusely in the membrane and cytoplasm and concentrated in nuclei of control myotubes, it was not targeted to these cellular compartments but was instead retained in a perinuclear distribution in myotubes expressing the mutant caveolin-3. (B) The nuclear fraction from control myotubes and myotubes expressing the TFT mutation were analyzed by western blotting for expression of Src. There was clearly diminished Src targeting to the nuclei of mutant myotubes. Actin was used as the loading control. (C) Equal amounts of protein from total cell lysates of control myotubes and myotubes expressing the TFT mutation were analyzed by western blotting for phosphorylation of Src at tyrosine 418 (pSrcY418) and total Src. Hyperphosphorylation of Src at this residue was observed in myotubes expressing the TFT mutation compared with control myotubes, while total cellular Src did not differ between the two cell populations.