Wild-type α-synuclein interacts with pro-apoptotic proteins PKCδ and BAD to protect dopaminergic neuronal cells against MPP+-induced apoptotic cell death

alpha-Synuclein is a pre-synaptic protein of unknown function that has been implicated in the pathogenesis of Parkinson's disease (PD). Recently, we demonstrated that 1-methyl-4-phenylpyridinium (MPP+) induces caspase-3-dependent proteolytic activation of PKC delta, which subsequently contributes to neuronal apoptotic cell death in mesencephalic dopaminergic neuronal cells [50,96]. In the present study, we examined whether PKC delta interacts with alpha-synuclein to modulate MPP+-induced dopaminergic degeneration. Over-expression of wild-type human alpha-synuclein in mesencephalic dopaminergic neuronal cells (N27 cells) attenuated MPP+-induced (300 mu M) cytotoxicity, release of mitochondrial cytochrome c, and subsequent caspase-3 activation, without affecting reactive oxygen species (ROS) generation. Wild-type alpha-synuclein over-expression also dramatically reduced MPP+-induced caspase-3-mediated proteolytic cleavage of PKC delta, whereas overexpression of the mutant human alpha-synuclein(A53T) did not alter the PKC delta cleavage under similar conditions. Immunoprecipitation-kinase assay revealed reduced PKC delta kinase activity in wild-type alpha-synuclein over-expressing cells in response to MPP+ treatment. Wild-type alpha-synuclein over-expression also rescued mesencephalic dopaminergic neuronal cells from MPP+-induced apoptotic cell death, while alpha-synuclein(A53T) exacerbated the MPP+-induced DNA fragmentation. Furthermore, co-immunoprecipitation studies revealed that alpha-synuclein interacts with the pro-apoptotic proteins PKC delta and BAD, but not with the anti-apoptotic protein Bcl-2 following MPP+ treatment. We also observed that the interaction between PKC delta and alpha-synuclein does not involve direct phosphorylation. Together, our results demonstrate that wild-type alpha-synuclein interacts with the pro-apoptotic molecules BAD and PKC delta to protect dopaminergic neuronal cells against neurotoxic insults. (c) 2005 Elsevier B.V. All rights reserved.