How oxidative metabolism modulates effects of ionizing radiation is incompletely understood. Because mitochondria participate in oxidative metabolism, we investigated the modulation of mitochondrial protein import and membrane potential (Δψ) in irradiated cells. Our data show that effects at low dose cannot be predicted from effects at high dose. When density-inhibited normal human fibroblasts were exposed to a toxic dose of 4 Gy, protein import into mitochondria isolated from these cells was decreased. In contrast, protein import into mitochondria isolated from low-dose-irradiated (10 cGy) cells was enhanced, suggesting that mitochondria may play a crucial role in low-dose-induced adaptive responses. At high dose, import defects were not solely due to changes in mitochondrial Δψ, and modulation of import was not tightly linked to the cellular capacity to repair radiation damage. Another striking observation is that in proliferating nonirradiated cells, mitochondrial protein import and Δψ were regulated in a cell cycle-dependent manner, being lower in S phase than in G1. Interestingly, when quiescent G0/G1 phase cells exposed to high-dose radiation were stimulated to proliferate, events associated with S phase, but not G1, significantly affected import. The strategy described here may serve as novel end points to study radiation-induced effects.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Clinical Biochemistry
- Cell Biology