Abstract 1395: Mitochondrial ATP-Binding Cassette Protein-1 (mABC1) Plays a Role in Mitochondrial Iron Homeostasis and Protein Export
Mitochondria are known to play an important role in regulating cell death and survival. We have demonstrated that overexpression of a novel mitochondrial protein, the mitochondrial ATP-binding cassette protein 1 (mABC1), protects neonatal rat cardiomyocytes (NRCM) against oxidant-induced cell death. However, the mechanisms by which mABC1 exerts these protective effects and the primary function of this protein are not known. The yeast homolog of mABC1, Mdl1p, has been shown to play a role in mitochondrial iron homeostasis and peptide export. Based on these observations and that Fe/S proteins contain iron, we hypothesized that the primary function of mABC1 is to export Fe/S clusters attached to their target protein/peptide out of the mitochondria. To test this hypothesis, we downregulated or upregulated mABC1 in NRCM, and measured mitochondrial non-heme iron and protein/peptide levels. We showed that the levels of mitochondrial non-heme iron were significantly decreased in a dose-dependent manner in NRCM transduced with mABC1 adenovirus compared with green fluorescent protein (GFP)-transduced cells (non-heme iron levels of 67.9 ± 15.7 vs. 80.2 ± 19.0 ng/100 μg mitochondrial protein for mABC1 vs. GFP- transduced cells; P <0.05). We then measured mitochondrial protein and large peptide levels in response to mABC1 downregulation using RNA interference. Cells with lower levels of mABC1 displayed a significantly higher amount of mitochondrial protein and peptide levels (33.4 ± 7.2% increase in mABC1- compared to control- siRNA transduced cells; P<0.05). Since mitochondrial iron is a source of oxidative stress, we also assessed the effects of mABC1 overexpression on the production of reactive oxygen species (ROS) using mitoSOX fluorescent marker. ROS production was markedly reduced in cells overexpressing mABC1 compared to the control (71.3 ± 4.7% less fluorescence in mABC1- compared to GFP-transduced cells; P < 0.05). These results demonstrate that mABC1 plays a role in mitochondrial iron homeostasis and peptide export, suggesting that it may be involved in the transport of Fe/S proteins out of mitochondria. Furthermore, its cytoprotective effects may be through regulating mitochondrial iron, which is a source of ROS and cellular damage.