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

Abstract 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 Cδ (PKCδ) contributes to the degenerative process in dopaminergic neurons. The Parkinsonian toxin MPP + activated caspase-3 and proteolytically cleaved PKCδ into catalytic and regulatory subunits, resulting in persistent kinase activation in mesencephalic dopaminergic neuronal cells. The caspase-3 inhibitor Z-DEVD-FMK and the caspase-9 inhibitor Z-LEHD-FMK effectively blocked MPP + -induced PKCδ proteolytic activation. To characterize the functional role of PKCδ activation in MPP + -induced dopaminergic cell death, RNAi-mediated gene knockdown was performed. Among four siRNAs designed against PKCδ, two specifically suppressed PKCδ expression. The application of siRNA abolished the MPP + -induced PKCδ activation, DNA fragmentation, and tyrosine hydroxylase (TH)-positive neuronal loss. Together, these results suggest that proteolytic activation of PKCδ may be a critical downstream event in the degenerative process of Parkinson's disease.