Cancer cells expressing the mitochondrially enriched EGFRvIII mutant are more resistant to apoptosis. A, Generation of U87MG stable transfectant cell lines that express EGFRvIII-MTS1 and EGFRvIII-MTS2. Western blotting shows that the three isogenic cell lines express equivalent levels of the transgenes. B,C, The EGFRvIII-MTS1 mutant is enriched in the mitochondria as shown by immunofluorescence staining and confocal microscopy (B) and cell fractionation/western blotting (C). D, Stability of EGFRvIII and EGFRvIII-MTS1 proteins is similar. Protein half-life study using transcription inhibitor cycloheximide determined the two proteins to have similar degradation rates.