DJ-1 is a multifunctional protein that performs functions in transcriptional regulation and oxidative stress, and the loss of its function is believed to result in the onset of Parkinson's disease (PD). In this study, we report that DJ-1 protects against UVinduced cell death through the suppression of the JNK1 signaling pathway. The results of both binding and kinase studies have revealed that MEKK1 is the direct target of DJ-1. The C-terminus of DJ-1 was crucial to the inhibition of the MEKK1 kinase activity. Wild-type DJ-1 sequesters MEKK1 within the cytoplasm and the L166P mutant facilitates the translocation of MEKK1 toward the nucleus without physical association. Both DJ-1 knockdown and pathogenic L166P mutant were determined to be highly susceptible to the UV-induced activation of the MEKK1-SEK1-JNK1 signaling cascade and cell death. Taken together, our findings show that missense mutation in DJ-1 sensitizes cells to stress-induced cell death through the MEKK1-SEK1-JNK1 signaling pathway, a process, which may trigger the early onset of PD.

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