α-Synuclein protects SH-SY5Y cells from dopamine toxicity

Dopaminergic human neuroblastoma SH-SY5Y cells were stably transformed to increase expression of α-synuclein, a Parkinson's disease-related protein. Transformed cells were more resistant to oxidative insults, showing a cytoprotective role of α-synuclein. The expression of redox chaperonins (DJ-1, HSP70, and 14-3-3) was evaluated by Western blotting. Expression of α-synuclein reduced HSP70 levels even in the presence of dopamine, with a twofold increase of DJ-1 in the absence of oxidants. DJ-1 is significantly reduced by dopamine, and even more by dopamine and Cu(II). Increased α-synuclein expression did not affect 14-3-3, although dopamine increased its level by 60% in wild-type cells. α-Synuclein not only upregulated DJ-1, but also shifted all DJ-1 forms to a single spot at pI = 5.7 not observed in wild-type cells. Dopamine gradually restored the distribution of DJ-1 forms to a situation similar to wild-type cells, with the form at pI = 6.1 progressively enriched under oxidative conditions.