FIGURE 3: CcO is incorporated into mitochondrial SCs in GBM cells with acquired radioresistance. (A) CcO activity in radiosensitive (U251, D456, and Jx39) and isogenic radioresistant (U251-RR, D456-RR, and Jx39-RR) cell lines. Data are presented as the mean ± SEM (n=4). (B) Representative Western blot showing the expression of the COX4 isoforms COX4-1 and COX4-2 in the radiosensitive and radioresistant cells. COX-I was probed as a loading control. (C) Digitonin-solubilized mitochondria from radiosensitive and radioresistant cell lines were subjected to BN-PAGE followed by complex I and IV IGA assays and Western blot for complex III. Representative image from 3 separate experiments. p < 0.0001 (****), calculated by Student t-test.