Growing evidence suggests that oxidative stress is involved in the neuronal degeneration and can promote the aggregation of a-synuclein. However, the role of a-synuclein under physiological and pathological conditions remains poorly understood. In the present study, we examined the possible interaction between the a-synuclein and oxidative stress. In a dopaminergic cell line MES23.5, we have found that the 200 mu M H2O2 treatment induced the translocation of a-synuclein from cytoplasm to nuclei at 30 min post-treatment. The immunoactivity of a-synuclein became highly intensive in the nuclei after 2 h treatment. The protein translocated to nucleus was a 10 kDa fragment of C-terminus region of alpha-synuclein, while full-length a-synuclein remained in cytoplasm. Thioflavine-S staining suggested that the C-terminal fragment in the nuclei has no beta-sheet structures. Our present results indicated that 200 mu M H2O2 treatment induces the intranuclear accumulation of the C-terminal fragment of a-synuclein in dopaminergic neurons, whose role remains to be investigated. (c) 2006 Elsevier Inc. All rights reserved.