Upon mitochondrial depolarization, Parkin, a Parkinson disease-related E3 ubiquitin ligase, translocates from the cytosol to mitochondria and promotes their degradation by mitophagy, a selective type of autophagy. Here, we report that in addition to mitophagy, Parkin mediates proteasome-dependent degradation of outer membrane proteins such as Tom20, Tom40, Tom70, and Omp25 of depolarized mitochondria. By contrast, degradation of the inner membrane and matrix proteins largely depends on mitophagy. Furthermore, Parkin induces rupture of the outer membrane of depolarized mitochondria, which also depends on proteasomal activity. Upon induction of mitochondrial depolarization, proteasomes are recruited to mitochondria in the perinuclear region. Neither proteasome-dependent degradation of outer membrane proteins nor outer membrane rupture is required for mitophagy. These results suggest that Parkin regulates degradation of outer and inner mitochondrial membrane proteins differently through proteasome- and mitophagy-dependent pathways.
Introduction: Recently, importance of D-amino acids in mammals has been drawing attention. D-Amino acids are enantiomers of L-amino acids and have been recognized as biomarkers and bioactive substa...
Abstract Mitochondria are believed to have originated from the endosymbiosis of bacteria and they still contain their own genome, which is called mitochondrial DNA (mtDNA). Under fluorescence microscopy of cultured mammalian cells, mtDNA is observed as numerous tiny dot-like structures called mitochondrial nucleoids. In live-imaging, the morphology and distribution of nucleoids are change dynamically, but the molecular details remain poorly understood. In this study, we constructed a custom siRNA library targeting 1,164 human mitochondria-related genes, and from live-imaging-based screening of HeLa cells, we identified that mitochondria calcium uniporter (MCU), a pore-forming subunit of the mitochondrial Ca2+ channel, is involved in nucleoid morphology. We found that suppression of MCU by RNAi induced the formation of highly enlarged nucleoids as well as respiratory dysfunction and that the re-introduction of MCU or treatment with Ca2+ ionophore recovered the enlarged nucleoid morphology. These results suggest that mitochondrial Ca2+ uptake via MCU is associated with nucleoid morphology. The constructed siRNA library might be widely applied to analyze the roles of mitochondrial proteins in various cellular events, making it useful to understand the multifaceted functions of mitochondria in human cells.
