Mitochondrial localization of DJ‐1 leads to enhanced neuroprotection

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Abstract
Mutations in DJ‐1 (PARK7) cause recessively inherited Parkinson's disease. DJ‐1 is a multifunctional protein with antioxidant and transcription modulatory activity. Its localization in cytoplasm, mitochondria, and nucleus is recognized, but the relevance of this subcellular compartmentalization to its cytoprotective activity is not fully understood. Here we report that under basal conditions DJ‐1 is present mostly in the cytoplasm and to a lesser extent in mitochondria and nucleus of dopaminergic neuroblastoma SK‐N‐BE(2)C cells. Upon oxidant challenge, more DJ‐1 translocates to mitochondria within 3 hr and subsequently to the nucleus by 12 hr. The predominant DJ‐1 species in both mitochondria and nucleus is a dimer believed to be the functional form. Mutating cysteine 106, 53, or 46 had no impact on the translocation of DJ‐1 to mitochondria. To study the relative neuroprotective activity of DJ‐1 in mitochondria and nucleus, DJ‐1 cDNA constructs fused to the appropriate localization signal were transfected into cells. Compared with 30% protection against oxidant‐induced cell death in wild‐type DJ‐1‐transfected cells, mitochondrial targeting of DJ‐1 provided a significantly stronger (55%) cytoprotection based on lactate dehydrogenase release. Nuclear targeting of DJ‐1 preserved cells equally as well as the wild‐type protein. These observations suggest that the time frame for the translocation of DJ‐1 from the cytoplasm to mitochondria and to the nucleus following oxidative stress is quite different and that dimerized DJ‐1 in mitochondria is functional as an antioxidant not related to cysteine modification. These findings further highlight the multifaceted functions of DJ‐1 as a cytoprotector in different cellular compartments.