Suppression of caspase-3-dependent proteolytic activation of protein kinase Cδ by small interfering RNA prevents MPP+-induced dopaminergic degeneration

The cellular mechanisms underlying the neurodegenerative process in Parkinson's disease are not well understood. Using RNA interference (RNAi), we demonstrate that caspase-3-dependent proteolytic activation of protein kinase Cdelta (PKCdelta) contributes to the degenerative process in doparninergic neurons. The Parkinsonian toxin MPP+ activated caspase-3 and proteolytically cleaved PKCdelta into catalytic and regulatory subunits, resulting in persistent kinase activation in mesencephalic doparninergic neuronal cells. The caspase-3 inhibitor Z-DEVD-FMK and the caspase-9 inhibitor Z-LEHD-FMK effectively blocked MPP=-induced PKCdelta proteolytic activation. To characterize the functional role of PKCdelta activation in MPP+-induced dopaminergic cell death, RNAi-mediated gene knockdown was performed. Among four siRNAs designed against PKCdelta, two specifically suppressed PKCdelta expression. The application of siRNA abolished the MPP+-induced PKCdelta activation, DNA fragmentation, and tyrosine hydroxylase (TH)-positive neuronal loss. Together, these results suggest that proteolytic activation of PKCdelta may be a critical downstream event in the degenerative process of Parkinson's disease. (C) 2004 Elsevier Inc. All rights reserved.