Common anti-apoptotic roles of parkin and a-synuclein in human dopaminergic cells Yutaka Machida a,b , Tomoki Chiba b , Atsushi Takayanagi f , Yoshikazu Tanaka b,c , Masato Asanuma d , Norio Ogawa d , Akihiko Koyama e , Takeshi Iwatsubo e , Shosuke Ito h , Poul Hening Jansen g , Nobuyoshi Shimizu f , Keiji Tanaka b , Yoshikuni Mizuno a , Nobutaka Hattori a, * a Department of Neurology, Juntendo University School of Medicine, Tokyo, Japan b Department of Molecular Oncology, The Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan c Department of Veterinary Hygiene, Nippon Veterinary and Animal Science University, Tokyo, Japan d Department of Brain Science, Okayama University Graduate School of Medicine and Dentistry, Okayama, Japan e Department of Neuropathology and Neuroscience, Graduate School of Pharmaceutical Sciences, University of Tokyo, Japan f Department of Molecular Biology Keio University, Tokyo, Japan g Department of Neurology, Zlekenhuls Gelderse Vallei, Edo, Netherlands h Fujita Health University School of Health Sciences, Aichi, Japan Received 17 April 2005 Available online 30 April 2005 Abstract Parkin, a product of the gene responsible for autosomal recessive juvenile parkinsonism (AR-JP), is an important player in the pathogenic process of ParkinsonÕs disease (PD). Despite numerous studies including search for the substrate of parkin as an E3 ubiq- uitin–protein ligase, the mechanism by which loss-of-function of parkin induces selective dopaminergic neuronal death remains unclear. Related to this issue, here we show that antisense knockdown of parkin causes apoptotic cell death of human dopaminergic SH-SY5Y cells associated with caspase activation and accompanied by accumulation of oxidative dopamine (DA) metabolites due to auto-oxidation of DOPA and DA. Forced expression of a-synuclein (a-SN), another familial PD gene product, prevented accu- mulation of oxidative DOPA/DA metabolites and cell death caused by parkin loss. Our findings indicate that both parkin and a-SN share a common pathway in DA metabolism whose abnormality leads to accumulation of oxidative DA metabolites and subsequent cell death. Ó 2005 Elsevier Inc. All rights reserved. Keywords: Parkin; Apoptosis; Antisense; Knockdown; Neuroblastoma; Synuclein dopamine metabolism; Quinone ParkinsonÕs disease (PD) is the second most com- mon neurodegenerative disorder primarily caused by selective loss of dopaminergic neurons in the midbrain substantia nigra pars compacta. Familial PD has been highlighted to study the mechanisms underlying neuro- degeneration in PD, although only 5–10% of patients with PD are of the familial form of PD [1,2]. To date, 10 causative genes have been mapped and cloned in familial PD by linkage studies, which have significantly enhanced our understanding of the genetic mechanisms of PD [3]. Of these genes, parkin, the causative gene (PARK2) of AR-JP, representing the most prevalent form of familial PD [4], is of special interest, because it encodes an E3 ubiquitin–protein ligase [5], which 0006-291X/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2005.04.124 * Corresponding author. Fax: +81 3 5800 0547. E-mail address: nhattori@med.juntendo.ac.jp (N. Hattori). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 332 (2005) 233–240 BBRC