title: Proteasome inhibitor-induced apoptosis is mediated by positive feedback amplification of PKCdelta proteolytic activation and mitochondrial translocation.
abstract: Emerging evidence implicates impaired protein degradation by the ubiquitin proteasome system (UPS) in Parkinson's disease; however cellular mechanisms underlying dopaminergic degeneration during proteasomal dysfunction are yet to be characterized. In the present study, we identified that the novel PKC isoform PKCdelta plays a central role in mediating apoptotic cell death following UPS dysfunction in dopaminergic neuronal cells. Inhibition of proteasome function by MG-132 in dopaminergic neuronal cell model (N27 cells) rapidly depolarized mitochondria independent of ROS generation to activate the apoptotic cascade involving cytochrome c release, and caspase-9 and caspase-3 activation. PKCdelta was a key downstream effector of caspase-3 because the kinase was proteolytically cleaved by caspase-3 following exposure to proteasome inhibitors MG-132 or lactacystin, resulting in a persistent increase in the kinase activity. Notably MG-132 treatment resulted in translocation of proteolytically cleaved PKCdelta fragments to mitochondria in a time-dependent fashion, and the PKCdelta inhibition effectively blocked the activation of caspase-9 and caspase-3, indicating that the accumulation of the PKCdelta catalytic fragment in the mitochondrial fraction possibly amplifies mitochondria-mediated apoptosis. Overexpression of the kinase active catalytic fragment of PKCdelta (PKCdelta-CF) but not the regulatory fragment (RF), or mitochondria-targeted expression of PKCdelta-CF triggers caspase-3 activation and apoptosis. Furthermore, inhibition of PKCdelta proteolytic cleavage by a caspase-3 cleavage-resistant mutant (PKCdelta-CRM) or suppression of PKCdelta expression by siRNA significantly attenuated MG-132-induced caspase-9 and -3 activation and DNA fragmentation. Collectively, these results demonstrate that proteolytically activated PKCdelta has a significant feedback regulatory role in amplification of the mitochondria-mediated apoptotic cascade during proteasome dysfunction in dopaminergic neuronal cells.
authors.affiliation: Parkinson's Disorder Research Laboratory, Iowa Center for Advanced Neurotoxicology, Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA.
authors.forename: Faneng
authors.initials: F
authors.lastname: Sun
authors.forename: Arthi
authors.initials: A
authors.lastname: Kanthasamy
authors.forename: Chunjuan
authors.initials: C
authors.lastname: Song
authors.forename: Yongjie
authors.initials: Y
authors.lastname: Yang
authors.forename: Vellareddy
authors.initials: V
authors.lastname: Anantharam
authors.forename: Anumantha G
authors.initials: AG
authors.lastname: Kanthasamy
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001483:Base Sequence; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002460:Cell Line; D025461:Feedback, Physiological; D007976:Leupeptins / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D061988:Proteasome Inhibitors; D051745:Protein Kinase C-delta / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D007976:Leupeptins; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D034741:RNA, Small Interfering; D025801:Ubiquitin; D051745:Protein Kinase C-delta; C505410:Casp3 protein, rat; C506435:Casp9 protein, rat; D053148:Caspase 3; D053453:Caspase 9; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde