Date Published: March 5, 2013
Publisher: Public Library of Science
Author(s): Hiroki Kato, Qiping Lu, Doron Rapaport, Vera Kozjak-Pavlovic, Orian S. Shirihai. http://doi.org/10.1371/journal.pone.0058435
PTEN induced kinase 1 (PINK1) is a serine/threonine kinase in the outer membrane of mitochondria (OMM), and known as a responsible gene of Parkinson’s disease (PD). The precursor of PINK1 is synthesized in the cytosol and then imported into the mitochondria via the translocase of the OMM (TOM) complex. However, a large part of PINK1 import mechanism remains unclear. In this study, we examined using cell-free system the mechanism by which PINK1 is targeted to and assembled into mitochondria. Surprisingly, the main component of the import channel, Tom40 was not necessary for PINK1 import. Furthermore, we revealed that the import receptor Tom70 is essential for PINK1 import. In addition, we observed that although PINK1 has predicted mitochondrial targeting signal, it was not processed by the mitochondrial processing peptidase. Thus, our results suggest that PINK1 is imported into mitochondria by a unique pathway that is independent of the TOM core complex but crucially depends on the import receptor Tom70.
Mitochondria are unique organelles which harbor numerous metabolic pathways and supply cells with energy in the form of ATP. The complex biogenesis and dynamics of the mitochondrial network necessitate elaborate quality control measurements to assure that damaged proteins and organelles are eliminated. A dysfunction of mitochondria causes fragmentation of the mitochondrial network and can induce a specific autophagy of mitochondrial fragments (also called mitophagy) , , .
In this study we addressed the participation of the TOM complex in PINK1 import using doxycycline inducible shRNA cell lines and by blocking the TOM import channel. We observed that Tom70 is essential for PINK1 import, whereas Tom40 appeared not to be involved in this process. In addition, although we did not obtain complete depletion of Tom22, our results might suggest that Tom20 and Tom22 are also not required for the import of PINK1. Lazarou et al. showed that the TOM core complex, including Tom40, Tom20, and Tom22 forms a complex with PINK1 on depolarized mitochondria . When mitochondria lose membrane potential, PINK1 accumulates on the OMM, and then recruits Parkin. Interestingly, PINK1/TOM complex did not contain Parkin. Hence, it seems that PINK1 associated with the TOM complex lost the ability to recruit Parkin. Accordingly, we speculate that TOM core complex regulates the binding between PINK1 and Parkin rather than import of PINK1 into the mitochondria.