Human Molecular Genetics Advance Access originally published online on August 13, 2009
Human Molecular Genetics 2009 18(22):4317-4328; doi:10.1093/hmg/ddp384
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Parkin selectively alters the intrinsic threshold for mitochondrial cytochrome c release
1 Neurology, Brigham and Women's Hospital, Boston, MA 02115, USA, 2 Harvard Medical School, Boston, MA 02115, USA, 3 Neurimmune Therapeutics AG, Schlieren, Switzerland and 4 Dana Farber Cancer Institute, Boston, MA 02115, USA
* To whom correspondence should be addressed at: Harvard Institutes of Medicine, Room 764, 77 Avenue Louis Pasteur, Boston, MA 02115, USA. Tel: +1 6175255185; Fax: +1 6175255252; Email: mlavoie{at}rics.bwh.harvard.edu
Received April 28, 2009; Revised July 3, 2009; Accepted August 10, 2009
Autosomal-recessive mutations in the Parkin gene are the second most common cause of familial Parkinson's disease (PD). Parkin deficiency leads to the premature demise of the catecholaminergic neurons of the ventral midbrain in familial PD. Thus, a better understanding of parkin function may elucidate molecular aspects of their selective vulnerability in idiopathic PD. Numerous lines of evidence suggest a mitochondrial function for parkin and a protective effect of ectopic parkin expression. Since mitochondria play a critical role in cell survival/cell death through regulated cytochrome c release and control of apoptosis, we sought direct evidence of parkin function in this pathway. Mitochondria were isolated from cells expressing either excess levels of human parkin or shRNA directed against endogenous parkin and then treated with peptides corresponding to the active Bcl-2 homology 3 (BH3) domains of pro-apoptotic proteins and the threshold for cytochrome c release was analyzed. Data obtained from both rodent and human neuroblastoma cell lines showed that the expression levels of parkin were inversely correlated with cytochrome c release. Parkin was found associated with isolated mitochondria, but its binding per se was not sufficient to inhibit cytochrome c release. In addition, pathogenic parkin mutants failed to influence cytochrome c release. Furthermore, PINK1 expression had no effect on cytochrome c release, suggesting a divergent function for this autosomal recessive PD-linked gene. In summary, these data demonstrate a specific autonomous effect of parkin on mitochondrial mechanisms governing cytochrome c release and apoptosis, which may be relevant to the selective vulnerability of certain neuronal populations in PD.
Present address: Neurimmune Therapeutics AG, Wagistrasse 13, 8952 Schlieren, Switzerland. 
These authors contributed equally.