[Abstract unavailable

Phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1) and PARK2/Parkin mutations cause autosomal recessive forms of Parkinson's disease. Upon a loss of mitochondrial membrane potential (ΔΨ m ) in human cells, cytosolic Parkin has been reported to be recruited to mitochondria, which is followed by a stimulation of mitochondrial autophagy. Here, we show that the relocation of Parkin to mitochondria induced by a collapse of ΔΨ m relies on PINK1 expression and that overexpression of WT but not of mutated PINK1 causes Parkin translocation to mitochondria, even in cells with normal ΔΨ m . We also show that once at the mitochondria, Parkin is in close proximity to PINK1, but we find no evidence that Parkin catalyzes PINK1 ubiquitination or that PINK1 phosphorylates Parkin. However, co-overexpression of Parkin and PINK1 collapses the normal tubular mitochondrial network into mitochondrial aggregates and/or large perinuclear clusters, many of which are surrounded by autophagic vacuoles. Our results suggest that Parkin, together with PINK1, modulates mitochondrial trafficking, especially to the perinuclear region, a subcellular area associated with autophagy. Thus by impairing this process, mutations in either Parkin or PINK1 may alter mitochondrial turnover which, in turn, may cause the accumulation of defective mitochondria and, ultimately, neurodegeneration in Parkinson's disease.autophagy | Parkinson's disease | phosphatase and tensin homolog-induced putative kinase 1 T he common neurodegenerative disorder Parkinson's disease (PD) occasionally can be inherited (1, 2). Parkinson disease 6/ phosphatase and tensin homolog (PTEN)-induced putative kinase-1 (PARK6/PINK1) is among the gene products associated with familial PD (2, 3). This 581-amino acid polypeptide is localized to the mitochondria and has only a single recognized functional domain, a serine/threonine kinase with a high degree of homology to that of the Ca 2+ /calmodulin kinase family. Overexpression of WT PINK1 rescues abnormal mitochondrial morphology that has been described in Drosophila carrying Pink1 mutations (4, 5), a finding that supports the notion that the mutated allele gives rise to a loss-of-function phenotype. Loss-offunction mutations in the gene encoding PARK2/Parkin (an E3 ubiquitin ligase) also can cause an autosomal recessive form of familial PD (2, 6). Parkin is thought to operate within the same molecular pathway as PINK1 to modulate mitochondrial dynamics (4, 5, 7). This possibility is intriguing, because Parkin has been reported to be essentially cytosolic (8, 9). However, we have shown that PINK1 spans the outer mitochondrial membrane, with its kinase domain facing the cytoplasm (10). These details of PINK1 topology are relevant to the reported Parkin/PINK1 genetic interaction because they place the only known functional domain of PINK1 in the same subcellular compartment as Parkin.However, the role played by Parkin, PINK1, or both in mitochondrial dynamics is still uncertain. Perhaps, the beginning of an answer to th...

Mutations in PTEN-induced putative kinase 1 (PINK1) are a cause of autosomal recessive familial Parkinson's disease (PD). Efforts in deducing the PINK1 signaling pathway have been hindered by controversy around its subcellular and submitochondrial localization and the authenticity of its reported substrates. We show here that this mitochondrial protein exhibits a topology in which the kinase domain faces the cytoplasm and the N-terminal tail is inside the mitochondria. Although deletion of the transmembrane domain disrupts this topology, common PD-linked PINK1 mutations do not. These results are critical in rectifying the location and orientation of PINK1 in mitochondria, and they should help decipher its normal physiological function and potential pathogenic role in PD.parkin ͉ Parkinson's disease ͉ mitochondria ͉ topology P arkinson's disease (PD), the second most common neurodegenerative disorder, is a sporadic condition that can occasionally be inherited (1). The rationale for studying the rare genetic forms of PD is based on the phenotypic similarity between the familial and sporadic forms of the disease, implying that the two share important pathogenic mechanisms. Among the different gene products associated with familial PD (2), PTEN-induced putative kinase-1 (PINK1) is localized to the mitochondria (3-10), an organelle strongly linked to PD pathogenesis. Although recessively inherited PD mutations in PINK1 are found throughout the protein, they are most commonly found in the only recognized functional domain of PINK1 (3,11,12), which is a serine/threonine kinase domain similar to that in the Ca 2ϩ /calmodulin kinase family (13,14). Overexpression of wild-type PINK1 can rescue the phenotype caused by PINK1 mutations in Drosophila (15, 16), supporting the notion that the mutated allele gives rise to a loss-of-function phenotype.Human PINK1 is a 581-aa polypeptide with a predicted N-terminal mitochondrial targeting signal (MTS), consistent with the observation that PINK1 localizes to mitochondria (Fig. 1A) (3-10). Loss-of-function mutations in the gene encoding parkin (an E3 ubiquitin ligase) cause the most frequent forms of recessive familial PD (17). In Drosophila, parkin is thought to operate within the same molecular pathway as PINK1 to modulate mitochondrial morphology (15,16,18), an intriguing observation given the fact that parkin has been reported to essentially be cytosolic (19).Both the subcellular and submitochondrial locations of PINK1 and the authenticity of its reported substrates have been controversial. Although it is agreed that PINK1 is a mitochondrialtargeted protein, PINK1 has been reported to reside in the inner mitochondrial membrane (IMM) (6,7,9,20), the mitochondrial intermembrane space (IMS) (6,8,9), the outer mitochondrial membrane (OMM) (7), and even the cytoplasm (21-24). Furthermore, the tumor necrosis factor type 1 receptor-associated protein (TRAP1) and the serine protease HtrA2/Omi have been identified as putative PINK1 substrates (8, 9). Although TRAP1 is localized mainly i...

Parkinson disease (PD) is a common adult-onset neurodegenerative disorder. Typically, PD is a sporadic neurological disorder and over time, affected patients see their disability growing and their quality of life declining. Oxidative stress has been hypothesized to be linked to both the initiation and the progression of PD. Pre-clinical findings, from both in vitro and in vivo experimental models of PD, suggest that the neurodegenerative process starts with otherwise healthy neurons being hit by some etiological factors, which sets into motion a cascade of deleterious events. In these models, initial molecular alterations in degenerating dopaminergic neurons include increased formation of reactive oxygen species presumably originating from both inside and outside of the mitochondria. In the MPTP mouse model of PD, time-course experiments suggest that oxidative stress is an early event which may directly kill some of the dopaminergic neurons. In this model, it seems that oxidative stress may play a greater role in the demise of dopaminergic neurons indirectly by activating intracellular cell death-related molecular pathways. As the neurodegenerative process evolves in the MPTP mouse model, indices of neuroinflammation develop such as microglial activation. The latter increases the level of oxidative stress to which the neighboring compromised neurons are subjected to, thereby promoting their demise. However, these experimental studies have also shown that oxidative stress is not the sole deleterious factor implicated in the death of dopaminergic neurons. Should a similar multifactorial cascade underlie dopaminergic neuron degeneration in PD, then the optimal therapy for this disease may have to rely on a cocktail of agents, each targeting a different critical component of this hypothesized pathogenic cascade. If correct, this may be a reason why neuroprotective trials using a single agent such as an antioxidant have thus far generated disappointing results.

PINK1 is a mitochondrial kinase proposed to have a role in the pathogenesis of Parkinson's disease through the regulation of mitophagy. Here, we show that the PINK1 main cleavage product, PINK1 52, after being generated inside mitochondria, can exit these organelles and localize to the cytosol, where it is not only destined for degradation by the proteasome but binds to Parkin. The interaction of cytosolic PINK1 with Parkin represses Parkin translocation to the mitochondria and subsequent mitophagy. Our work therefore highlights the existence of two cellular pools of PINK1 that have different effects on Parkin translocation and mitophagy.