Identification Of Nuclear-encoded Proteins In Mitochondrial Localization And DNA Damage Repair

Mitochondria, the important organelle in eukaryotic cells, is involved in many aspects of cellular activities, including aerobic metabolism, apoptosis and autophagy, reactive oxygen species production, etc. Among the proteins that regulate mitochondrial function, only a few are encoded by its own genome and most come from nuclear including all mitochondrial DNA damage repair-related proteins. Accumulating data has demonstrated that mitochondrial dysfunction due to mutations can cause mitochondrial diseases in humans. In this study, both bioinformatics analysis and molecular biology techniques are utilized to search the mitochondrial proteins that are potentially important in maintaining mitochondrial genome stability. We first limited the candidates only functioning in nuclear DNA damage repair. Through nuclear export signal (NES) and mitochondrial targeting signal (MTS) prediction combined with data of their co-localization with mitochondria, we have identified a list of genes that are potentially involved in mitochondria DNA damage repair. ERCC2, a gene related to human Xeroderma pigmentosum occurrence and mainly involved in NER(nucleic excision repair) pathway in the nuclear, was chosen for further study mainly because it is an important DNA damage repair protein and its role in mitochondria is largely unknown. From our study, we identified a MTS signal located at its N-terminal and further demonstrated its co-localization with mitochondria in the cytoplasm. In U2OS cells with a high level of ERCC2protein, shRNA-mediated knock down of its expression leads to a substantially increased level of ROS production. Overall, our results provide the evidence that ERCC2protein is present in mitochondria and may play an important role in mitochondrial DNA damage repair.